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View Full Version : Pair of polyester stitch and tape dinghies again -UK sources for unguents and mat



dylan winter
12-12-2016, 10:46 AM
Well, it seems that we are going to build a pair of these

http://www.selway-fisher.com/NCoble9p3.jpg

http://www.selway-fisher.com/Cobles.htm

I am going to cover the joints both in and out with polyester and glass tape or chopped mat.

the boats are going to be painted not varnished. These are dinghies to dump on the hard.

I have a couple of questions

does anyone have any recommendations for UK source of polyester and hardner?

What spec am I after - I want 15 minutes of working time at ten degrees C or so

then I want the stuff to go off even at low temperatures so that we can get a move on with the next bit.

UK source of tape - or should I use chopped mat and cut everything to shape - I prefer this idea - what weight of chopped mat?

In another thread some-one mentioned treating the ply with something to help make the Polyester stick to the wood properly.

The plan is to knock up a pair of these in a week. I will blog each day's progress

Two men, a bandsaw and a cold shed in January.

The plan is to use 6mm ply and door architrave.

I am not bothered at how rough the finish is - the aim is to make a couple of dinghies that will tow well, row well and can tolerate being dragged across a shingle beach. They have also got to be light enough for one sixty year old bloke to get the the dinghy onto and off the roof - so no bouyancy - the aim is to make the shells as light, stiff and as cheap as we can.

thanks Chaps - you are a marvelous resource.

D

please feel free to tell me that I am fool to use polyester and that I should really invest in some shed heat and spend a bit more money on Epoxy

all I would say is that price and speed speak volumes. Jon and I are both 60 so longevity of the dinghy is not an issue

artif
12-12-2016, 10:58 AM
CFS or Cornish fibre sports

skaraborgcraft
12-12-2016, 11:08 AM
East Coast Fibreglass are a bit closer, but i always shopped in CFS as they were on the doorstep. ECF have given good service with mail order stuff to Sweden also. I reccomend both, shipping cost probably wont be much different.

dylan winter
12-12-2016, 11:39 AM
East Coast Fibreglass are a bit closer, but i always shopped in CFS as they were on the doorstep. ECF have given good service with mail order stuff to Sweden also. I reccomend both, shipping cost probably wont be much different.

thanks for that

now that opens up a whole new can of worms

quite a few to choose from

http://www.ecfibreglasssupplies.co.uk/c-1005-polyester-resins.aspx

http://www.ecfibreglasssupplies.co.uk/c-356-cloth-fabric-and-tapes.aspx

any guidance gratefully recieved

D

P.I. Stazzer-Newt
12-12-2016, 12:32 PM
Everything you need is available from a good roofing supplier.

Glasplies is reasonable and I've used them in the past. - Ditto Easy Composites http://www.easycomposites.co.uk/

What do you plan to do with Chopped strand mat? - traditionally you'd just tape the joints.

dylan winter
12-12-2016, 12:45 PM
Everything you need is available from a good roofing supplier.

Glasplies is reasonable and I've used them in the past. - Ditto Easy Composites http://www.easycomposites.co.uk/

What do you plan to do with Chopped strand mat? - traditionally you'd just tape the joints.

I thought I could cut it to shape - It might be a cheaper.

maybe I am deluded.

The aim is to do the stitch and tape junctions both inside and outside. There is the inner stem, the transom, the thwarts, the outer stem and forefoot and the skegs to laminate into place.

Anyone want to make a stab at the initial quantities of mat and unguent we should order

D

skaraborgcraft
12-12-2016, 12:47 PM
I only buy the Lloyds approved stuff. I have used re-blended stuff in the past on some bulk filling non critical boat work, but given the cheapo price, stick with the Lloyds stuff,

skaraborgcraft
12-12-2016, 12:51 PM
http://www.ecfibreglasssupplies.co.uk/p-1777-fibreglass-tape-200g-x-75-mm.aspx

I dunno what Paul suggests on the plans, maybe 2 layers of 75mm off set, its what i used on the DK18, over fillets. The open canoe i built nearly 10 years ago used to 50mm tape and Lloyds resin.......still in one peice.

P.I. Stazzer-Newt
12-12-2016, 01:44 PM
75 to 100 metres of 50mm tape 10 kilos of resin catalyst to match.

I have cut strips of CSM for joints - tape is much much nicer, though I have heard of people cutting strips of woven fabric "on the bias"

skaraborgcraft
12-12-2016, 02:07 PM
Depending on the boat and the finish required, some dont like the selvedge edge that tape leaves, needs bogging and sanding to make it dissappear......dont think Dylan will be too worried about that, and cutting fabric or matt can be a real PIA if you have to cut a few hundred meters! You will use more stanley blades cutting your fabric than the extra cost of the tape...i reckon.

Whameller
12-12-2016, 04:31 PM
Another vote for East Coast Fibreglass; the are excellent and very good VFM.

Cutting up CSM or woven rovings to use for the seams would be a real PITA (as skaraborgcraft says) and would slow you down a lot; a false economy - tape is pretty cheap. If you are worried about the selvedge edge, use biax tape.

As to quantities, the Selways Fisher plans usually have notes which tell you what you need.

Cable ties (the diddy small one) work well as ties for the joints.

dylan winter
12-12-2016, 05:14 PM
Depending on the boat and the finish required, some dont like the selvedge edge that tape leaves, needs bogging and sanding to make it dissappear......dont think Dylan will be too worried about that, and cutting fabric or matt can be a real PIA if you have to cut a few hundred meters! You will use more stanley blades cutting your fabric than the extra cost of the tape...i reckon.

okay - tape it is then

how wide?

D

dylan winter
12-12-2016, 05:15 PM
75 to 100 metres of 50mm tape 10 kilos of resin catalyst to match.

I have cut strips of CSM for joints - tape is much much nicer, though I have heard of people cutting strips of woven fabric "on the bias"

is that for both boats or just for one

D

dylan winter
12-12-2016, 05:26 PM
next question

how should I attach the inner and outer gunwhale.

can I use polyester to stick they in place?

How do I do that - should I screw them as well. Self driving SS screws from screwfix have worked

Cascamite?

Epoxy?

and another question

is there a simple way of getting the clinker style overlaps - how time consuming would it be to get them

D

boat fan
12-12-2016, 05:38 PM
next question

how should I attach the inner and outer gunwhale.

can I use polyester to stick they in place?

How do I do that - should I screw them as well. Self driving SS screws from screwfix have worked

Cascamite?

Epoxy?

and another question

is there a simple way of getting the clinker style overlaps - how time consuming would it be to get them

D


Epoxy Dylan.

Simple way to get clinker laps ?
Not if you are taping them.

Cloth and tape do not like sharp corners to bend around and they don`t want to stay there lying flat.

You need to radius the outside corners and the inside one, ( lots of fillet there alone ) laborious and fiddly and time consuming.

dylan winter
12-12-2016, 05:45 PM
Epoxy Dylan.

Simple way to get clinker laps ?
Not if you are taping them.

Cloth and tape do not like sharp corners to bend around and they don`t want to stay there lying flat.

You need to radius the outside corners and the inside one, ( lots of fillet there alone ) laborious and fiddly and time consuming.

I think you just talked me out of it

D

Zuri
12-12-2016, 05:59 PM
Hey Dylan,

I think you might be over complicating this. If you like the clinker style overlaps - just do that. Use epoxy and drywall screws until the epoxy sets. No clamps, no tape.

It's really pretty simple. The only trade off is that you'll need a couple station molds to hold things together while you cut the rolling bevel (that sounds harder than it is - just a simple block plane and a few minutes per strake). I'd much rather deal with that then trying to tape and fair all those seams.

I prefer the lapstrake look too.

Travis.

boat fan
12-12-2016, 06:01 PM
Hey Dylan,

I think you might be over complicating this. If you like the clinker style overlaps - just do that. Use epoxy and drywall screws until the epoxy sets. No clamps, no tape.

It's really pretty simple. The only trade off is that you'll need a couple station molds to hold things together while you cut the rolling bevel (that sounds harder than it is - just a simple block plane and a few minutes per strake). I'd much rather deal with that then trying to tape and fair all those seams.

I prefer the lapstrake look too.

Travis.

Must agree with Zuri there.Y>

dylan winter
12-13-2016, 02:16 AM
Hey Dylan,

I think you might be over complicating this. If you like the clinker style overlaps - just do that. Use epoxy and drywall screws until the epoxy sets. No clamps, no tape.

It's really pretty simple. The only trade off is that you'll need a couple station molds to hold things together while you cut the rolling bevel (that sounds harder than it is - just a simple block plane and a few minutes per strake). I'd much rather deal with that then trying to tape and fair all those seams.

I prefer the lapstrake look too.

Travis.

Can I tape the inside of the laps?

and I assume that we would have to be really accurate with cutting the panels - I was hoping that with trad stitch and tape we could be a slightly less precise with the cutting

I will have a look at the plans once our wives have agreed to let us build these dinghies.

the problem with epoxy - apart from the price - is the temperature in our shed. Working on the snot tender with polyester was so easy despite the temperature and the damp

besides I love an experiment

D

skaraborgcraft
12-13-2016, 02:30 AM
I made epoxy lap joints on the Poddy pram. It is a damn sight quicker than taping inside and out.

http://forum.woodenboat.com/showthread.php?161613-Half-size-Trug-Poddy-Pram-dinghy

You could do the same without epoxy, but you would be better having an inside batten to screw to, and use a cascamite or polyurethane type glue or tube of stickum. It mighte still be quicker than a tape seam boat, but there is a lot of shape to be beveled into stringers on that particular hull. You could try out a scale cardboard model when you get the plans. Tape seam came along to get rid of all the need for fussy woodwork. On a dinghy this size, how much time will you save?

P.I. Stazzer-Newt
12-13-2016, 02:42 AM
I'd not use cascamite (extramite) on anything that stays damp - it's fine for occasional immersion but needs to be dry stored.


MIL-TFD.41

dylan winter
12-13-2016, 02:57 AM
I'd not use cascamite (extramite) on anything that stays damp - it's fine for occasional immersion but needs to be dry stored.


MIL-TFD.41


thanks for that

so can we use polyester to stick the inner and out gunwhales to the top of the top panels

skaraborgcraft
12-13-2016, 02:59 AM
One of the advatages of taped seam is that all that endgrain is embedded in glass and resin, your exposed laps will not get that protection, and might be worth thinking about if you are intending a rough service life. You could make a hybrid of taped seams below the waterline, and lapped above, i am using that form on the "13" build, also a mix of epoxy, polyester and screw on batten, in order to keep the build at the lowest cost.

skaraborgcraft
12-13-2016, 03:00 AM
thanks for that

so can we use polyester to stick the inner and out gunwhales to the top of the top panels

I would not use polyester to stick any wood to wood joints.....its not a glue in that sense.

P.I. Stazzer-Newt
12-13-2016, 03:01 AM
thanks for that

so can we use polyester to stick the inner and out gunwhales to the top of the top panels
I would not do that - but you're welcome to try.

dylan winter
12-13-2016, 03:01 AM
I made epoxy lap joints on the Poddy pram. It is a damn sight quicker than taping inside and out.

http://forum.woodenboat.com/showthread.php?161613-Half-size-Trug-Poddy-Pram-dinghy

You could do the same without epoxy, but you would be better having an inside batten to screw to, and use a cascamite or polyurethane type glue or tube of stickum. It mighte still be quicker than a tape seam boat, but there is a lot of shape to be beveled into stringers on that particular hull. You could try out a scale cardboard model when you get the plans. Tape seam came along to get rid of all the need for fussy woodwork. On a dinghy this size, how much time will you save?


https://lh4.googleusercontent.com/-Eia0V-NZhXc/UWbOoBlNOqI/AAAAAAAAAs0/xsYSOwCn29Q/s576/trug%2520pram%2520032.jpg


the seams on your pram above

can I make those by taping the inside and then running some polyester down into the gaps from the oustide. With the little snot tender I think the clinker edges really help to keep her nose out of the water.

skaraborgcraft
12-13-2016, 03:20 AM
I dont think i would do it that way, seems like twice the work and materials when it could just be done with just an epoxy glue line. It might certainly be worth an experiment, my glued lap joints on the "13" have been made with just a modified PVA with a D3 rating (exterior), but is backed up with gripfast. screws.
I might be tempted to glue the lap, bog the gap with poly and then tape the inside seam. How cold is this garage? I cant use any glue below 5 degrees except polyurethane.

dylan winter
12-13-2016, 03:40 AM
I dont think i would do it that way, seems like twice the work and materials when it could just be done with just an epoxy glue line. It might certainly be worth an experiment, my glued lap joints on the "13" have been made with just a modified PVA with a D3 rating (exterior), but is backed up with gripfast. screws.
I might be tempted to glue the lap, bog the gap with poly and then tape the inside seam. How cold is this garage? I cant use any glue below 5 degrees except polyurethane.

ambient for east anglia

so three degrees at night and about eight during the day.

I do have some flood lights that I can use to raise the temperature locally.

Al G
12-13-2016, 03:45 AM
https://lh4.googleusercontent.com/-Eia0V-NZhXc/UWbOoBlNOqI/AAAAAAAAAs0/xsYSOwCn29Q/s576/trug%2520pram%2520032.jpg


the seams on your pram above

can I make those by taping the inside and then running some polyester down into the gaps from the oustide. With the little snot tender I think the clinker edges really help to keep her nose out of the water.

I naively tried that with epoxy and it ran down the channels and out over the planks. It has to be filleting thickness to stay put and therefore must be tooled into the gaps.

artif
12-13-2016, 03:49 AM
A couple of these keep my shed (not insulated) warm enough for epoxy/glues, throughout winter,. Cheap to run and no naked flames / exposed elements.
I'm currently sticking a deck hatch together with epoxy, without any problem, down here in deepest, darkest and cold Kent.
http://www.toolstation.com/shop/Heating/d230/Electric+Heaters+%26+Dryers/sd3168/Tubular+Heater/p32265

skaraborgcraft
12-13-2016, 04:39 AM
ambient for east anglia

so three degrees at night and about eight during the day.

I do have some flood lights that I can use to raise the temperature locally.

I use a halogen light heater when it gets close to freezing, but its more local heat than a warm enviroment.

https://lh3.googleusercontent.com/doMdTbd4Ca-EUDu87yJ2u4XxM68ovoteCIgqmb-2vk5t-OhEKcmcjP8NUzZGWDyFsATxr1rBQdY7M8TOhhUsbfTXN1gf9Uy ZV_26gg=w1024-h600-no

You can always throw a heavy tarp or cover over the area you are glueing up just to help retain some heat. You might have more luck keeping a small garage warm than i have keeping temps up.

Zuri
12-13-2016, 12:10 PM
Just keep the temporary screws in a little longer to keep things together until the epoxy sets up enough to hold. You don't need tape or even much precision - epoxy is your friend here. Add wood flour for gluing things together and as a gap filler.

So 3 deg C = 38 deg F and 8 deg C = 46 deg F for us yanks. Using fast cure epoxy, you'll still be able to pull the screws the following day. I've done epoxy work in these temps. It's not a big deal. It will set up enough and will post cure fully later.

Unless you are a glutton for punishment, and really want to tape in that cold while being fumigated with polyester resin which may or may not work out. It would be entertaining though.

Travis.

dylan winter
12-13-2016, 12:33 PM
Just keep the temporary screws in a little longer to keep things together until the epoxy sets up enough to hold. You don't need tape or even much precision - epoxy is your friend here. Add wood flour for gluing things together and as a gap filler.

So 3 deg C = 38 deg F and 8 deg C = 46 deg F for us yanks. Using fast cure epoxy, you'll still be able to pull the screws the following day. I've done epoxy work in these temps. It's not a big deal. It will set up enough and will post cure fully later.

Unless you are a glutton for punishment, and really want to tape in that cold while being fumigated with polyester resin which may or may not work out. It would be entertaining though.

Travis.

when you get to 60 everything in the shed is done for the entertainment value

I love an experiment

D

Zuri
12-13-2016, 12:37 PM
when you get to 60 everything in the shed is done for the entertainment value

I love an experiment

D

Subscribed.

DeniseO30
12-13-2016, 12:41 PM
http://www.westsystem.com/ss/cold-temperature-bonding/

Zuri
12-13-2016, 03:01 PM
D
Are you doing the 9'-4" or 10'-6" version?
Are you scarfing? or butt blocks for the planks?
Travis.

dylan winter
12-13-2016, 03:11 PM
D
Are you doing the 9'-4" or 10'-6" version?
Are you scarfing? or butt blocks for the planks?
Travis.

sweet pea is 9 foot 4 and is perfect

she is from a mold taken from a local dinghy in keyhaven - a large shingle harbour in the solent

http://www.visitmyharbour.com/harbours/solent/keyhaven/

butt joints - quicker, easier, stronger

Can I just use polyester to hold those in place. What about if I put a layer of chopped mat under the covering piece

D

Zuri
12-13-2016, 03:37 PM
I don't have the plans. It's hard to tell if there is a stem - or just panels stitched together at the bow.

http://www.selway-fisher.com/NCoble9p3.jpg


For laminating the stem and gluing the butt blocks to the strakes, I would use epoxy.

You can probably get away with the polyester and tape for the strake seams. However, it's not really an adhesive, so I wouldn't use it for the butt blocks or stem. Titebond II or III would probably be a better choice for these areas if you are not going the epoxy route.

I'd also stack and coordinate the butt blocks all at the center thwart - it has the least curve (for establishing fairness) and would look better than having random blocks sticking out here and there in your interior.

I imagine for speed and simplicity, you are not going to install flotation chambers?

Travis.

dylan winter
12-13-2016, 04:14 PM
I don't have the plans. It's hard to tell if there is a stem - or just panels stitched together at the bow.

http://www.selway-fisher.com/NCoble9p3.jpg


For laminating the stem and gluing the butt blocks to the strakes, I would use epoxy.

You can probably get away with the polyester and tape for the strake seams. However, it's not really an adhesive, so I wouldn't use it for the butt blocks or stem. Titebond II or III would probably be a better choice for these areas if you are not going the epoxy route.

I'd also stack and coordinate the butt blocks all at the center thwart - it has the least curve (for establishing fairness) and would look better than having random blocks sticking out here and there in your interior.

I imagine for speed and simplicity, you are not going to install flotation chambers?

Travis.

That is a good reason for having them in the middle

my guess they will add stiffness if not strength

I am going to do a test panel sticking two bits of ply together with a pad of chopped mat in the middle and see how strong that it compared to an equal sized blob of epoxy

as for the stem

I reckon that a taped bow might work

the mat and unguent is great in tension so I reckon that is should hold the bow together

I shall see

the aim is to use fenders for floatation as on sweet pea.



https://www.youtube.com/watch?v=-Z7gQValP7w They act as bumpers, a spray skirt and can be removed before hefting onto the roof. It also makes sense to me to have floatation on the outside - the inside is for stuff and people.

I will also make up a set of slatted floorboards - also removable

like the duck punt

https://www.youtube.com/watch?v=CdrmZpcCJ4o

John Meachen
12-13-2016, 05:00 PM
What about using this for sticking the wood together? http://www.tradefixdirect.com/sealants-adhesives-etc/all-adhesives/pu-wood-glue As for a clinker type appearance,would the CLC lapstitch approach be adaptable?

dylan winter
12-13-2016, 05:14 PM
What about using this for sticking the wood together? http://www.tradefixdirect.com/sealants-adhesives-etc/all-adhesives/pu-wood-glue As for a clinker type appearance,would the CLC lapstitch approach be adaptable?

have you tried it?

D

DeniseO30
12-13-2016, 05:32 PM
Dylan, I see this stated many times on forums like this.

"I am going to do a test panel sticking two bits of ply together with a pad of chopped mat in the middle and see how strong that it compared to an equal sized blob of epoxy".

A glued ply lapstrake hull essentially becomes mono hull like, unlike a clinker build that is designed for "movement"

Poly-o sticks, epoxy bonds. ALSO, moisture gets under poly-o

dylan winter
12-13-2016, 05:36 PM
Dylan, I see this stated many times on forums like this."
"
I am going to do a test panel sticking two bits of ply together with a pad of chopped mat in the middle and see how strong that it compared to an equal sized blob of epoxy".
A glued ply lapstrake hull essential becomes mono hull like, unlike a clinker build that is designed for "movement"
Poly-o sticks, epoxy bonds. ALSO, moisture gets under poly-o

I am a simple minded man

I do not understand what you have just written

D

Zuri
12-13-2016, 06:22 PM
OK Dylan,

I know I'll sound like a broken record and I'm campaigning the benefits of epoxy here almost as much as you campaign the joys of duck punting but here goes.

Weight:

How much weight do you think you'll add by layering tape using polyester? vs - no tape. Just fit the planks and epoxy fillet them - done. No tape. No unnecessary weight. You gotta get that thing up on top of the Polo. I'm thinking no tape is better here.

Time:

You saw Skaraborgcraft's thread - he planked the entire dink in a couple enjoyable hours. You don't even have to bevel the planks if you don't want to. You can use temporary screws to hold things together. It won't matter if the epoxy sets up in 1 hr or 24.

And - you get that sexy clinker look

No going back and redoing the joints with tape after assembly. Or, rounding over all the edges so they'll take the tape, then deal with the aggravation if the tape still doesn't decide to cooperate and leaves you with a bunch of white bubbled pocks all over your newly minted joints when you're not looking.


Cost:

The extra cost of epoxy vs polyester might be offset by not using tape. I think the added cost of the tape, and certainly the time it would take to install it, and fair it would outweigh just using epoxy fillets.


General:

And then there's the proven track record with this type of construction, the multi use ability to use it for gluing the butt blocks, laminating the stem. It's designed for use as an adhesive, a laminate and a resin. Then there is the longevity. Also, - being cooped up in a cold shed smelling the polyester resin (not my idea of an enjoyable week).

So, I've stated my case. I'm rooting for you. Feel free to disregard anything said above and march to the beat of your own drum. If it's adventure you're after - I'll still follow.

Travis.

Frank!
12-13-2016, 07:05 PM
Hi Dylan,
"Have you tried" - baling Sweet Pea from a fully swamped condition?
Regards,
Frank

dylan winter
12-14-2016, 12:14 PM
Hi Dylan,
"Have you tried" - baling Sweet Pea from a fully swamped condition?
Regards,
Frank

No,

but I have deliberatly swamped it and I can stand up and wave for help or drift to the nearest shore or paddle it with a single oar to the nearest moored boat or shoreline

The only time I sail her is within 50 yards of the shore

just like the duck punt

so for me, and the way I use my tender, a stable swamping is fine - I can always get to shore

you would be amazed, when sailing, how 15 stone man sitting on the bottom of a nine foot dinghy improves the stability. The sail I use is from an Optimist dinghy - sailed by kids

Finally, of course I have a life jacket on.

The aim is to create a shell as light as possible - I can remove the fenders and floor boards when I need to lift it onto the car.

I have really enjoyed the little snot tender this past year - best 100 I ever spent on a boat

apart from a duck punt of course

D

Whameller
12-14-2016, 05:10 PM
Hi Dylan,

Several others have already said variants of this, but:

- Polyester resin is optimised for laminating (laying up GRP hulls, sheathing, etc), not glueing wood together
- You can, in ideal conditions, use it for glueing wood - but the wood needs to be very carefully prepared and temperature and humidity kept within fairly tight parameters (RTFI on the pot).
- Polyester resin 'glued' wood assemblies are never as strong as those using sticky stuff designed for the purpose; they are also usually heavier
- As a wood 'glue' all that polyester resin offers as an advantage is that it is cheaper than epoxy; the rest is all negative.

So, given the conditions in which you intend to build your cobles and the use to which you intend to put yours, I wouldn't expect a polyester resin stitch and tape well-used tender to hold together for more than a couple of seasons at best; I wouldn't expect a polyester resin clinker ply structure to last even a season. I personally would build them with epoxy stitch and tape.

dylan winter
12-14-2016, 05:46 PM
Hi Dylan,

Several others have already said variants of this, but:

- Polyester resin is optimised for laminating (laying up GRP hulls, sheathing, etc), not glueing wood together
- You can, in ideal conditions, use it for glueing wood - but the wood needs to be very carefully prepared and temperature and humidity kept within fairly tight parameters (RTFI on the pot).
- Polyester resin 'glued' wood assemblies are never as strong as those using sticky stuff designed for the purpose; they are also usually heavier
- As a wood 'glue' all that polyester resin offers as an advantage is that it is cheaper than epoxy; the rest is all negative.

So, given the conditions in which you intend to build your cobles and the use to which you intend to put yours, I wouldn't expect a polyester resin stitch and tape well-used tender to hold together for more than a couple of seasons at best; I wouldn't expect a polyester resin clinker ply structure to last even a season. I personally would build them with epoxy stitch and tape.

I know you are a pro but

why will they fall apart?

Mirror dinghies are still hanging together 40 or fifty years on

I have seen a lot where the ply has rotted before the seams have gone

surely todays Polyester is as good/bad as the stuff we ued for building mirrors

The duck punt is four years old and still sound

D

http://mirrordiscussforum.org/pictures/to_zinnowitz.jpg

Andrew2
12-15-2016, 03:02 AM
If wood to wood like your gunnels, then PU adhesive, as long as the fit is half reasonable. The stuff they sell in the local B&Q even says 'can be used in boatbuilding' and goes off fast.

One idea is to glue lap it with poxy for the panel joints, held with drywall screws, then, when the hull is complete, chuck a tarp over it and put a couple of fan heaters in there and cook the whole thing. Working in a barn in Norfolk, we had a plastic box 'tent' on pulleys from the rafters, lowered it over the project and put a heater in if the ambient was too low.

Somewhere on this forum, there is a build of a SF coble. A few years ago and by a guy who was Canadian or French speaking, but in the US. Might be worth a search.

dylan winter
12-15-2016, 03:12 AM
If wood to wood like your gunnels, then PU adhesive, as long as the fit is half reasonable. The stuff they sell in the local B&Q even says 'can be used in boatbuilding' and goes off fast.

One idea is to glue lap it with poxy for the panel joints, held with drywall screws, then, when the hull is complete, chuck a tarp over it and put a couple of fan heaters in there and cook the whole thing.

Somewhere on this forum, there is a build of a SF coble. A few years ago and by a guy who was Canadian or French speaking, but in the US. Might be worth a search.



the gunwales are a fit of planed edge of architrave to ply so the fit will be perfect.

I have an isopon kit in the shed so I will do some test bits - and film me attempting to break them apart

D

skaraborgcraft
12-15-2016, 04:24 AM
Dylan, theres nowt wrong with polyester on ply when used in conjunction with tape, as your Mirror dinghy example. What is not so good is wood to wood joints, as already stated,its nowhere near as good as a D3 rated PVA or polyurethane glue. If you want lap topsides, you will have to chamfer the planks to get a good enough glue surface if you dont want to use epoxy, then you might have to double up on the inside tapes due to the wood you are removing, more weight and work than just using epoxy in the first place.
I would be more than happy to donate 1.5kg of epoxy resin which should be more than adequate for glueing laps, but they wont let me post noxious chemicals in the post from here.
I do not know of any "glued lap" boats built with polyester. If i thought it would work, i would have used it on the '13', as the budget for that build is almost non-existent. Polyester with tape, or epoxy, PVA, polyurethane glued laps. Im sure you can make a decent test sample that will be encouraging, but that might not behave the same way as a long plank polyester glue joint in a dinghy bunping alongside the mothership(fenders or not), or being dragged over rough ground, i can assure you it is brittle and non flexible when used as a gap filling bog......put some Isopon P40 (long strand glass filler) between to long flexible battens and see how it fairs before committing yourself.

Whameller
12-15-2016, 05:28 AM
I know you are a pro but

why will they fall apart?

Mirror dinghies are still hanging together 40 or fifty years on

I have seen a lot where the ply has rotted before the seams have gone

surely todays Polyester is as good/bad as the stuff we ued for building mirrors

The duck punt is four years old and still sound

D

http://mirrordiscussforum.org/pictures/to_zinnowitz.jpg
Because unless built in good conditions and with a lot of preparation, polyester resin - not being designed as a glue - won't stick wood to wood particularly well.

If you can keep your build space above about 15 degrees C and the relative humidity reasonably low during prep, glueing up and curing AND you make sure that the glueing surfaces are as large as possible, totally free of all contaminants (eg: greasy marks, sticky tape residue, other glue spots, etc) and well roughed up - then a polyester resin stitch & tape boat should stick together OK.

But:
- How do you achieve those conditions in an East Anglian garage in winter (I've lived in Cambridgeshire in the past !) ?
- There is a lot of extra work involved over and above either epoxy stitch & tape or epoxy clinker/ply.
- The end result will be heavier for you to get on/off your car.

Do you want 'OK' for a few seasons or something that you are really happy will survive at the end of your tow for a long time ? Your choice, just my thoughts - hopefully helpful.
Cheers !

Edward Pearson
12-15-2016, 06:31 AM
Dylan,

If I wanted to use polyester resin and make two boats, I'd coat a smooth or double chined tender without any tumblehome with mold release, take a mold off and use that to make two. Your making three boats that's all. GRP boatbuilding is the simplest of the lot. Mechanically fasten (screws/ trunnels) any wood trim to it. Flow coat the bilge with waxed left over gelcoat. For being naughty boys, a donation to the RNLI might at least equal things up. To minimise the amount of grp required to get the panels stiff enough, my eye would be drawn to a 'carvel' smooth pram tender at 9ft, that has inbuilt curvature stiffness at this small size. Will also be quiet alongside and not tink. You could mold off that green one, but all those chines will give you a ball ache unless given a large round over: the grp won't conform, the gelcoat unsupported will chip off later.

If you want to build an MDF/ wood mold, use one of three Gartside's free published pram tender plansets from Watercraft. Of the three, for a sailing tender, your most optimum and legit way would be to quickly strip one of these one weekend then mold off it and make two grp hulls. Rig and foils are shown so you can put the rig on without having ti work anything out. The 10ft one is better if your not going to sail it: it's slightly beamier on the waerline. The chined plywood one is shown stitich and tape but no rig. These plansets are free in WC. The SF Coble is a miniature boat not an optimised yacht's tender. Different thing.

http://store.gartsideboats.com/collections/dinghies-and-daysailers/products/8ft-sailing-rowing-pram-porgy-design-195

Glad to see the old green tender getting out and about!

Ed

dylan winter
12-15-2016, 11:17 AM
or this from the same bloke

more conventional


http://www.selway-fisher.com/Otherupto10.htm#WESTRAY

D

keyhavenpotterer
12-15-2016, 11:55 AM
The Westray is very nice. Was a comercially produced design. One at the club. Sweet little thing.

Edward Pearson
12-15-2016, 03:21 PM
or this from the same bloke

more conventional

http://www.selway-fisher.com/Otherupto10.htm#WESTRAY

D

Dylan my considered ruminations are that as a yacht tender evolves from a miniaturised dinghy it:

1. Has relatively slightly greater waterline and gunwale beam. Typically the length to beam ratio can maximise/ reach 2:1 combined with a flatter floor midsection. This distribution of displacement gives it more lateral stability more reserve lateral stability when stepping into it off the midline and greater potential load carrying ability. Downsides being slightly wetted area and wavemaking resistance.

2. A reduction in the forefoot below and relatively well above the waterline to avoid the tender tripping on it when it surfs and pitches in large following waves when the nose may dive. The waterlines generally will be blunter and convex/ trochoid forward giving it slightly greater resistance but perversely a greater entry angle slows the boat when being towed and reduces the risk of it sliding into the mothership.

3. The topsides forward are arranged to provide reserve buoyancy to provide more stability forward when stepping down into the boat forward. Dryness in relatively large waves for the boat size is also increased. Together with the reduction in forefoot, it can be achieved with a pram bow or scow bow. The scow bow preserves entry angle and a better reserve buoyancy entry angle in very large waves so it will be less easily stopped, at the expense of more loa. On the same Loa the pram bow will better preserve the interoarlock half beam for forward rowing when a passenger is sat aft so the weight is spread optimally either side if the lcb and ultimately the most maximised reserve buoyancy If the boat is drawn to a set loa.

4. An oar and motor tender will evolve a small quarter beam buttock angle. The flat run aft will enable planing if other conditions are met. The disadvantage will be greater wetted area under oar. A sail, motor and oar tender will tend to have a typical more trochoid aft waterplane when horizontal. Wetted area will be reduced under oar and slow froude speed motor use, and weather helm should be reduced as it heels under sail. In this regard blunt similarly trochoid forward sections and high (almost symmetrical to aft) levels of reserve buoyancy forward can make for a very balanced heeled fore and aft hull shape.

Andrew2
12-15-2016, 03:38 PM
Nother thought. While I like the Cobles, lots of panels if you are looking for a quick functionable build. Might be an idea to stick to three a side, or three with a flat bottom. Like the Westray. Just musing...

dylan winter
12-15-2016, 03:57 PM
Dylan my considered ruminations are that as a yacht tender evolves from a miniaturised dinghy it:

1. Has relatively slightly greater waterline and gunwale beam. Typically the length to beam ratio can maximise/ reach 2:1 combined with a flatter floor midsection. This distribution of displacement gives it more lateral stability more reserve lateral stability when stepping into it off the midline and greater potential load carrying ability. Downsides being slightly wetted area and wavemaking resistance.

2. A reduction in the forefoot below and relatively well above the waterline to avoid the tender tripping on it when it surfs and pitches in large following waves when the nose may dive. The waterlines generally will be blunter and convex/ trochoid forward giving it slightly greater resistance but perversely a greater entry angle slows the boat when being towed and reduces the risk of it sliding into the mothership.

3. The topsides forward are arranged to provide reserve buoyancy to provide more stability forward when stepping down into the boat forward. Dryness in relatively large waves for the boat size is also increased. Together with the reduction in forefoot, it can be achieved with a pram bow or scow bow. The scow bow preserves entry angle and a better reserve buoyancy entry angle in very large waves so it will be less easily stopped, at the expense of more loa. On the same Loa the pram bow will better preserve the interoarlock half beam for forward rowing when a passenger is sat aft so the weight is spread optimally either side if the lcb and ultimately the most maximised reserve buoyancy If the boat is drawn to a set loa.

4. An oar and motor tender will evolve a small quarter beam buttock angle. The flat run aft will enable planing if other conditions are met. The disadvantage will be greater wetted area under oar. A sail, motor and oar tender will tend to have a typical more trochoid aft waterplane when horizontal. Wetted area will be reduced under oar and slow froude speed motor use, and weather helm should be reduced as it heels under sail. In this regard blunt similarly trochoid forward sections and high (almost symmetrical to aft) levels of reserve buoyancy forward can make for a very balanced heeled fore and aft hull shape.

I could not have said it better myself!

keyhavenpotterer
12-20-2016, 05:05 AM
Westry 9 in build

https://www.facebook.com/SelwayFisherDesign/photos/a.1442548916060223.1073741828.1442489789399469/1710096655972113/?type=3

https://scontent-lhr3-1.xx.fbcdn.net/v/t1.0-9/15589663_1710096655972113_7683819775697147776_n.jp g?oh=9605c5afaf94b9abaff08e2792551fba&oe=58FAC6DF