Dinghy 'Pontoons' for Stability

[KAIROS]

To add stability and permanent floatation to a dinghy, I am adding 'pontoons' to each side. These canvas-over-foam tubes uwill run for about 5' of the boats 7' length. They will be clear of the water when the boat is lightly loaded, and will come into play when heavily loaded, half-full of water, or in the case of a suddenly imbalanced load toward one side.

The idea is much like the 'Dingy Dogs' shown here. These are too long, too big, and too ugly for my application. Also, I want something which will not deflate and is robustly secured to the boat yet can be removed. If the dinghy breaks loose from a tow line, sinks in a storm, and is washed up on the beach a month later, I want these pontoons to still be in place.

http://dinghydogs.com/Images/trinkarow.jpg

I like the idea of tubes of closed-cell foam with canvas covers. In this case the canvas will be black to match the color of the dinghy sheer strake. I will be using 6" diameter closed cell foam 'rods' inside the 5-ft. long canvas tubes. Attaching this gear is the issue.


This drawing, below, shows my current thinking......using boltropes which slide into long slots attached to the dinghy sheer strake. Another option is to put a rod in each edge of the canvas as shown but only attach this at intervals.....the rod would then stiffen the edges between the fittings that grab it at intervals.

I'm undecided as to how to secure the tubes of foam-filled canvas to the dinghy, so that they are very secure yet removable. The method of attachment determines how the canvas covers are made and vice-versa. Suggestions, ideas, comments are welcome.

Thanks.
http://www.yachtflyers.com/forum_images/dingy_floatation.gif

[Ian McColgin]

I put together a bad (to my eye) version of this for a friend's dink and he's happy but when I ever get around to it for my dink (project #13,746) I will solve two problems:

I was not happy with how the canvass fit and I now think it can't be put on tightly enough as you've drawn and as I did. Making it in two parts so that it can be sewn at top and bottom, leave the seam tab out will allow for a tighter and cleaner fit and the tab then becomes an easy attachment point.

My friend does not row his dink. I do. I need to arrange it to clear the oars which I think just some oar lock pads and my usual 8' oars will do. I also carry a "sideboard" - like a pivoting leeboard but on only the starboard side - to make it easy to handle the boat in a high wind. I need a way of either working that or simply leaving the float off in that area.

Anyway, it really does make the dink more totally useful.

G'luck

[mmd]

I saw one last year with pink pool noodles bolted to the sides. Surprising amount of reserve stability, but I'm not so sure of the colour scheme. Musta cost about ten bucks to install.

[uwhilna]

Dinghy pontoons as an afterthought in alloy

http://i538.photobucket.com/albums/ff350/fakeperson/Photo0010.jpg

[Lewisboats]

I used pool noodles slit on edge to create flotation on canoe outriggers. Worked a champ and I was able to use up to a 60 sf sail. Got lots of comments on them but they weren't pink. I've seen a wacky lassy with them on too, used as shear bumpers/flotation.

http://www.angelfire.com/ego/lewisboatworks/Stuff/Sail/spirit4.jpg

[KAIROS]

Thanks all.:)

I've edited post #1 to clarify what information, exactly, I am looking for. The question is mainly how to attach the 6" diameter, 5-ft long foam filled canvas tubes to the dinghy. I present one option in the drawing, but am hoping there might be a simpler method of attachment, or some fittings I can buy 'off-the-shelf'. Robustness and fairly easy removal are the requirements.

[skuthorp]

I've used pool noodles too on my Macgreggor, but on balance (?) I prefer a bit extra sand ballast. A friend built a trimaran conversion for his, but he has a young child. There was a metal dinghy about here with inflatable sponsons built on. Haven't seen one for a while.

[Lewisboats]

Why not straps and buckles?

[Ian McColgin]

If you sew it in a long D shape, one narrower flat panel and one wider bent, sewing the foam in with the second seam sewn pushing the whole taught and flat you're off to a good start. Then turn the two unfinished edges outside of each seam in on each other and sew that up so you have a nice long tab maybe 1/2" or less wide, 4 layers thick. This you can just screw into the hull with oval head screws and nice washers that fit spaced every 6" or so. If it's a thin glass hull, glue a wooden slat inside the hull and drive the screws into that. This will position it without shifting. And it will look good and trim.

[Don Kurylko]

How about something like this from You Know Where Marine? 8.5" x 3.25" x 6' long. Only $159.99 each! :eek:



http://images.westmarine.com/full/118320.jpg


Shock absorbers take the teeth out of docking obstacles

Closed-cell foam encased in a soft polyester textile cover protects your boat against contact damage. Unlike traditional vinyl or rubber, it won’t squeak or mar, and the high-density foam will never leak or become flat. Polyester cover is UV-, dirt- and abrasion-resistant. Cleans easily. Large, flexible mounting tabs conceal upper fasteners. Flexible enough to mount on curves or around corners.



Material: Polyester fabric/closed-cell foam
Attachment Method: #8 or #10 screws and finish washers or nails
Cross-Section Shape: D-shape
Shock Absorption Mechanism: Foam padding
Warranty: Three years

[KAIROS]

Why not straps and buckles?

My inner S&M says yes to that, but please, please, show or draw me a picture. Do I wear them or do I put them on the dinghy somehow?

[Lewisboats]

Through bolt with bronze machine screws or perhaps rivet with copper roves, bolt with ss bolts or however you want. Use webbing with plastic buckles so nothing corrodes. Best if your cover has sleeves so the webbing can go through the sleeve or loop, holding it positively in place rather than just loose around the bag. You could even make wood pads to glue to the hull with the ends of the webbing fastened to the pads...then you wouldn't have a thru hull hole. One strap every 2-3 ft would be sufficient I would think, but you would want a strap within 12" of each end then however many in the middle to keep it somewhat in line when the water pushes against it.

edited to add: A quick Google and this popped up...you should be able to find something that will work here: http://www.strapworks.com/ (http://www.strapworks.com/)
Velcro is an option too but buckles will last longer.

This looks promising: http://www.strapworks.com/Acetyl_Plastic_Cam_Straps_p/pcs112l.htm

http://www.strapworks.com/v/vspfiles/photos/PCS112L-2.jpg

[Paul Scheuer]

I think such devices are properly called sponsons and were used in early canoes. Some looked quite decent, taperred to the ends and removable. What I've seen were canvas covered framed and planked semi-circular section shapes. My impression is that they were marketing devices intended to counter any reservation of the basic canoe's perceived instability.

[Tom Robb]

I suppose it's irrelevant to point out that these are unspeakably ugly.
Of course you could always wear a mask when you use the dink....
Just sayin'

[Todd Bradshaw]

I have trouble seeing much value in covering ethafoam sponsons with canvas that will pretty soon become moldy. If it's natural canvas, it will rot away. If it's synthetic, it will turn green and get pretty nasty looking anywhere that it isn't getting enough ventilation. There are some synthetic meshes that would drain and dry a lot better, like Phifertex.

http://www.beaconfabric.com/vindex.html?cat82.htm

On the other hand, black ethafoam actually withstands the elements pretty well all by itself. My folks have a fiberglass Lincoln canoe that I got them around 1980 with exposed foam sponsons. It's been sitting outside on the beach for 30 years and the ethafoam is getting a little worn-looking, but still works fine. The big foam strips are essentially through-bolted to the hull. There are stiff plastic washers about 2" diameter under the heads of long #8 or #10 SS machine screws which pass through the foam and the hull. On the inside of the hull, there are small washers and cap nuts. The system is secure, weather resistant, not awful looking and the strips can be removed or replaced in a few minutes if desired.

http://www.canoesandkayaks.com/images/boats/sports_side.jpg

[Songololo]

Stowaway boats make use of inflatable buoyancy tubes. These are attached via straps fed through paired polyurethane bridges. What I mean by paired is that there is one on the outside, backed up by another on the inside of the hull. This allows the tubes to be mounted either inside or outside the boat.

Some pics...

Straps and bridges:

http://www.seahopper.co.uk/photos/assembly%20250px%20photos/L1040079.jpg

With buoyancy tube:

http://www.seahopper.co.uk/photos/assembly%20250px%20photos/L1040084.jpg


Here they are mounted outside:

http://www.seahopper.co.uk/photos/thames/thames_03_250px.jpg


Stowaway Boat's website (http://www.seahopper.co.uk/k2-webpages/assembly.html).

[KAIROS]

Thanks much for those ideas for these sponsons, folks! The straps would be pretty simple and easy to disassemble, if I go the route of fabric covered cylinders of foam. But then Todd comes along with his all-the-sudden so obvious solution. Now I'm on another google spree.


.......black ethafoam actually withstands the elements pretty well all by itself.....The system is secure, weather resistant, not awful looking and the strips can be removed or replaced in a few minutes if desired.

http://www.canoesandkayaks.com/images/boats/sports_side.jpg

I find that it is sold in planks which can be shaped. They could be rigged for easy removal without much engineering too. Even recycled materials.

I was considering a mesh-like fabric for the cover in my current scheme. Regardless of the type of foam or mounting, I'd like to cover it with some kind of synthetic fabric. Even if I glue it on. The look of canvas-like fabric is so much nicer than foam. It's for a 7'7" Nutshell pram, which fits on the cabin top of our sailboat. Reserve stability and buoyancy are now required. Trying to keep it not-so-ugly though:

http://www.yachtflyers.com/forum_images/nutshell_profile1.gif

http://www.yachtflyers.com/forum_images/nutshell_cabintop.gif

[mcdenny]

How about a new wider dinghy using your existing rudder, daggerboard, sail rig, etc. Building the hull is the easy part.

Heck, why not split it down the middle, add a 12" center section?

[seo]

Sponsons work well. I've had dinghies that have the canvas-covered foam neoprene, which looks good and holds up well, but costs a lot, and doesn't provide a lot of maintenance.
For a dinghy that's going to get chewed on in the dinghy-dock scrum, I might consider a strip of high-density pvc (or wood) on the outside of the foam to protect it from digs and abrasion. Also would make a good continuous washer-plate for the attaching bolts.
One problem with straps, buckles, etc is that if these are part of the boat's "stability profile" then they shouldn't be too easy to remove. That way they're more likely to be there when needed.

[KAIROS]

......One problem with straps, buckles, etc is that if these are part of the boat's "stability profile" then they shouldn't be too easy to remove. That way they're more likely to be there when needed.

Yes, I don't want to worry about them coming adrift though it's okay if they do so after the dingy is smashed to pieces. Those straps seem so handy though, and easy. But there's probably a way to make the through-bolts come off quick when I want to remove the sponsons......but fast removal is not the priority.

One feature....not the main one....of this sponson thing I didn't mention is that it makes the dinghy a reasonable coastal 'liferaft' for when I hit a rock and sink the sailboat. In my cruising area water temps are low enough that you have about a half hour in the water, before you can't even swim to the nearest island. You've got to get out of the water fast. A ways up the inside passage and the VHF is not even useful. Sure, technology like an EPIRB might save us, but I'd rather just get in the dingy and row a mile to shore.

An inflatable provides the added stability and buoyancy, but I just can't talk myself into one (looks, rowing, towing, etc). And a life raft is certainly overkill in this scenario. You just have to get out of the water and have some mobility. A bigger hard dinghy is too heavy for us and too big to stow aboard. A small dingy (which I have) with sponsons can stay upright and afloat in quite a chop in a harbor or after shipwreck.

A good boat without sponsons can do well too. But, I have some physical limitations now which make me not-so confident in small boat handling as I used to be....that's the main reason I need sponsons on my dinghy. And, a small dinghy like the Nutshell works for us.

This is all just background though. I'm not getting an inflatable, or a liferaft, or a bigger dinghy, or making my dinghy bigger. I'm putting sponsons on this Nutshell pram.

Thanks for the input!

[Lewisboats]

...for when I hit a rock and sink the sailboatPessimistic aren't Ya! :eek::D

[woodenMFV]

The Kajak solution and the blue inflatable strapped on's are good I think. If you want another material-idea: think about this "hard foam" they made surfboards of in the eighties / or for insulating houses. You can attach it directly with screws into behind-the-hull-glued nuts/washers...like your other shapes also.

Screws/ButterflyNuts/washers would be my attachment, to come back to your initial question.

[DGentry]

Pessimistic aren't Ya! :eek::D

Well . . . there are lots of rocks, and funky currents - and the water really is cold! The dinghy was always our back up plan, too (the first being not to hit any rocks).

Anyway, my suggestion is that 2-3 plastic fenders, lashed (horizontally) to the outside of each of the gunwales would serve the same purpose, would be tougher and less prone to mildew, and would actually look kind of salty, rather than ad hoc. Plus, of course, they make for good bumpers . . . .

Just a thought!

Dave Gentry

[KAIROS]

Pessimistic aren't Ya! :eek::D

Just a realist ;). There are rocks everywhere here. In shallow Florida, Chesapeake or Barnegat Bay, you run aground in the mud, hop out and shove off. Here, the bottom knocks a hole in the boat. A decidedly unfriendly bottom. New England too, of course. In the past you might have sunk in California too, but sinking is banned there now.

It's a good thing to be able to envision sinking.

[KAIROS]

.....my suggestion is that 2-3 plastic fenders, lashed (horizontally) to the outside of each of the gunwales...

Dave Gentry

That was my original plan. The hole-through-the-center type. I could have been done now too. The foam/canvas option is much cheaper. The new bumpers would have been at least $200. The foam/canvas is less than $100. I envision the foam/canvas as looking much better....if it ever gets done.

[wizbang 13]

glue 2" of pink foam to the BOTTOM and dynel over it

[wizbang 13]

sorry for my usual fast post.. stolen wifi... turning anchoage.. ect.. must post fast or loose typing

[KAIROS]

glue 2" of pink foam to the BOTTOM and dynel over it

But after I capsize I'd have to use a snorkel to breath since the boat would be more stable inverted ;).


sorry for my usual fast post.. stolen wifi... turning anchoage.. ect.. must post fast or loose typing

For a post of any length, to avoid it evaporating into cyber air, I type into software on my computer (Word, etc). When completely done, I copy and paste it here. Very little connection time needed.

[wizbang 13]

Kairos, If the dingy capsizes, it's still capsized wether it has flotation on the bottom or "bags" above the wl .But if it gets a hole , flotation in the bottom will keep the rails up. Flotation above the wl is not very effective.

[seo]

What if "Pink Foam?"
I have used blueboard styrofoam insulation for this, with glass/polyester. The blue board needs to be painted first (I used plain latex house paint) to keep the styrene from getting at the styrofoam. I also used a thin (1/4) sheet of luan plywood over the foam, under the glass, to distribute local loads better and keep from crushing the foam. Maybe pink foam has better physical properties than the blue stuff?
One of the great advantages of a double bottom (which 2" of foam on the bottom will give you) is that the boat can be left at the float or towed with the drain plug out. So even if it rains, or you get a lot of spray in while towing, it will stay dry because the bottom will have freeboard over the waterline when the boat's empty. This is the case with the Boston Whalers, including the "Squall" dinghy.
The problem with flotation in the bottom is that when the boat's tipped over it's pretty unstable. Sponsons at the waterline will only keep the rails above waterline, but will improve stability.
For el cheapo sponsons, I once bought a roll of "ethafoam," which is a quite strong, close-cell foam that's used in a lot of kayaks, and in some packaging for electronics. It's very durable. The roll I got was sold for fendering along a float or dock, and was about 3", half-round. It was much stronger than a "sea noodle" pool floatie. It wasn't very expensive, and would allow you to home-make the types of sponsons that they fit to the sides of canoes.

[John B]

I assume that this is doubling as a fender as well?
A lot of the seasons damage your boat will take is from your or other dinghies alongside and quite a bit of that will be from pounding up when a wake shoves it from astern up against the deadrise of the transom or counter . So some cover to the top of the outwhale/ gunwhale is good.
What I would do Kairos , is make some light ply patterns to match the shape of the dinghy top strake.A bit narrower though. Then I would drill an appropriate number of holes through the lower edge into that top strake ( as few as possible.. maybe 4) and come up with a gimmick that gives me a 'nut'. T nut say or epoxy some stainless nuts to the ply shape. Maybe there should be a light batten there as well to give the nuts some bite.

Then , shape some foam to match the strake/ pattern , contact glue it on and contact glue the fabric over that from an overlap on the bottom edge. Leave a free overlap at the top of foam and fabric which can be pulled over the gunwhale, folded and screw fastened through eyelets or batten to the inside of the gunwhale. Bolt the lower edge to the strake from the inside through the holes you drilled earlier. You can get small urethane washers which would help seal that point.

What you'd end up with is a professional looking , shaped and fabric covered bouyancy fender. It'd be nice to have some extra length for wrap around the bow and stern too.

[KAIROS]

thanks SEO et al.

I appreciate the idea of foam on the bottom. But......


Kairos, If the dingy capsizes, it's still capsized wether it has flotation on the bottom or "bags" above the wl .But if it gets a hole , flotation in the bottom will keep the rails up. Flotation above the wl is not very effective.

First, the location of floatation does matter as far as the orientation of the floating object, whether flotsam, dingy or person. This is why, for example, throw-able flotation cushions should not be worn on one's back.....in that position they tend to hold a floating person face down. If you want a capsized boat to turn turtle and want it to tend to stay that way, put flotation on the bottom or low down.

Second, sponsons above the waterline don't have much effect on a boat's performance, which is good since the boat was not designed for them. But when the boat heels dramically or is loaded down, they increase beam and begin to provide flotation.

The one way they these sponsons would affect performance is when sailing around the harbor. If heeled, the lee sponson will drag in the water.....but the tiny boat will be less likely to capsize. And of course when overloaded, both sponsons would cause drag but that's the tradeoff.

[KAIROS]

........For el cheapo sponsons, I once bought a roll of "ethafoam," which is a quite strong, close-cell foam that's used in a lot of kayaks, and in some packaging for electronics. It's very durable. The roll I got was sold for fendering along a float or dock, and was about 3", half-round. It was much stronger than a "sea noodle" pool floatie. It wasn't very expensive, and would allow you to home-make the types of sponsons that they fit to the sides of canoes.

I'm checking out the various forms of ethafoam or evafoam. It is cheap and can be shaped. I was hoping to find a source like packaging industry rather than anything boaty, for cost.

[KAIROS]

......What I would do Kairos , is make some light ply patterns to match the shape of the dinghy top strake.A bit narrower though. Then I would drill an appropriate number of holes through the lower edge into that top strake ( as few as possible.. maybe 4) and come up with a gimmick that gives me a 'nut'. T nut say or epoxy some stainless nuts to the ply shape. Maybe there should be a light batten there as well to give the nuts some bite.

Then , shape some foam to match the strake/ pattern , contact glue it on and contact glue the fabric over that from an overlap on the bottom edge. Leave a free overlap at the top of foam and fabric which can be pulled over the gunwhale, folded and screw fastened through eyelets or batten to the inside of the gunwhale. Bolt the lower edge to the strake from the inside through the holes you drilled earlier. You can get small urethane washers which would help seal that point...

Thanks. This is close to what I've been thinking and makes me think I might not be too far off-base. I'd rather not wrap over the rail though. I am thinking that I could let the flotation be a bit higher than the rail but stay outside. This could cause oar clearance problem but I can fix that.


....What you'd end up with is a professional looking , shaped and fabric covered bouyancy fender. It'd be nice to have some extra length for wrap around the bow and stern too.

I can't extend around to either transom. I barely have the length needed on the cabin top to store it at 7'7". I will put the standard canvas-on-foam rail guard there:

http://www.jamestowndistributors.com/userportal/woeimages/marinesupplies/large/4141-1.jpg

[John B]

In that case it becomes really simple eh;) I wish I could buy that fender here.. I had to make my own for the stripper last year.

4 or 5 mm ply patterns/ bases. use patterns to drill 6 to 8 holes in the top strake. glue gimmick.....nut/ t nut, threaded plate to bases maybe with a light batten included. glue foam to base and wrap and glue fabric around that . Bolt to strake. 6 to 8 bolts per side for removal. stiffer ply and more robust bolts/ nuts... it could be a little as 3 bolts per side?

[KAIROS]

In that case it becomes really simple eh;) I wish I could buy that fender here.. I had to make my own for the stripper last year.....

To clarify, that 'gunnel guard' shown above is not flotation....only an inch diameter of foam at most. But it is configured similar to what I was originally thinking in post #1 drawing. It's rediculously expensive....you might have made your own anyway.

The appealing look of that gunnel guard (post #34) is what I am striving for.......not as easy to achieve that look when the diameter of my flotation foam is relatively huge, but.....

[John B]

I realise that... this what I made for a soft fender out of plumbers pipe insulation and UV stickyback.

http://i227.photobucket.com/albums/dd48/Waione_photos/the%20strip%20dinghy/IMG_4884_1.jpg
just zip tied on for now. Due to come off again this winter for a proper varnish job.

[seo]

Things that both the pipe-insulation and canvas-covered foam neoprene that sticks up over the top of the rail do:
1) Get in the way of oars, which isn't insurmountable, but takes a bit of fooling with.
2) Protects both the dinghy and the boat when the dinghy gets up under the stern overhang. This is also a problem on transom-stern boats like my old H-28 with a lot of flare in the stern. The only boats that seem pretty immune are powerboats with flat transom sterns, and maybe short-ended double enders.

[Cuyahoga Chuck]

A lot of work with dubious potential. .
The naval architect, Jacques Mertens, designed the D4/D5 as the dinghy for his 40' sailboat. It's an S&G 8' pram with three box-section seats that are completely sealed with epoxy. There is so much trapped air in it it won't sink. Ever. No muss no fuss.
This is the sailboat version so the front seat has been replaced with a mast bench.
http://gallery.bateau2.com/displayimage.php?album=343&pos=13
It will never be as pretty as a Nutshell Pram but you can't have everything.

[wizbang 13]

I haven't seen any boston whalers cruising by upside down lately.

[snow(Alan H)]

The good old 'Walker Bay' is perfect (but not classic in appearance)

http://i408.photobucket.com/albums/pp165/Alanh22/P1130794-1.jpg;

http://i408.photobucket.com/albums/pp165/Alanh22/warkworth2510063_2.jpg

[KAIROS]

A lot of work with dubious potential. . ....

I understand that there are simpler and better looking ways to make a boat unsinkable than putting sponsons on (similar to the Walker Bay dinghy above). But, what I will achieve with sponsons is making the boat:

(1) 'unsinkable' (nothing is) AND
(2) unlikely to capsize AND
(3) easier to board if flooded.

Flotation built into the bottom will only help make it (1) unsinkable. Flotation built into seats take care of the unsinkable issue and contributes to (3) since the flotation is higher than if it were in the bottom.

However, flotation in the bottom or seats doesn't help make the boat less likely to (2) capsize, and any flotation added lower than the boat's upright center of buoyancy doesn't help the boat be (3) easier to board when flooded.

(by the way, a boston whaler would probably want to stay upside-down :eek: if it were flooded and rolled in a sea, because of how the flotation is distributed)