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Thread: SOF estuary dinghy

  1. #1
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    Default SOF estuary dinghy

    I'm looking for the right boat design.

    I often holiday in Salcombe in Devon which has a lovely estuary with several sandy coves. I'm envious of the vast number of Zodiac/Avon RIBs and SIBs buzzing around. So much quicker than getting ferries and treks along a coast path to get to a nice cove. They can also stay after the ferry closes and aren't bothered about staying on a beach that is cut off by the tide! Salcombe is a drowned river valley to be precise which means wherever we stay is up a steep hill from the water - 10-20% gradients!

    My Dad lives on the Exe estuary (also in Devon) which is a more typical estuary with a huge expanse of water when the tide is in and mud flats when the tide is out. His house is 250m from the water but flat terrain.

    So my brief is:
    1. Most likely skin on frame - It needs to be lightweight so it can easily car top and wheel up/down a hill to the water. I'm thinking of a wheeled dolley that I sling underneath just like SIBs pulled up the beach. Something as light as a SOF could also be stored in the garden/parking area of a holiday rental cottage.
    2. Flat-ish bottom for landing on a beach and good stability for ferrying 3 people across the estuary with a small outboard - just like a SIB.
    3. Sharp bow and V bottom for good sailing in choppy estuary waters, which is why I haven't simply gone out and bought a SIB!


    So far I'm thinking of adapting an established plan for SOF techniques with a ply bottom.

    These seem like good candidates:


    As I see it, I have a trade off between a good sailor and a flat bottomed plodder good for the ferry duties. I do like the look of the Highlander 10, while the Monfort Cartopper needs no adaptation for SOF. So many choices!!! ....

  2. #2
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    Default Re: SOF estuary dinghy

    Quote Originally Posted by Salcombe View Post
    I'm looking for the right boat design.

    I often holiday in Salcombe in Devon which has a lovely estuary with several sandy coves. I'm envious of the vast number of Zodiac/Avon RIBs and SIBs buzzing around. So much quicker than getting ferries and treks along a coast path to get to a nice cove. They can also stay after the ferry closes and aren't bothered about staying on a beach that is cut off by the tide! Salcombe is a drowned river valley to be precise which means wherever we stay is up a steep hill from the water - 10-20% gradients!

    My Dad lives on the Exe estuary (also in Devon) which is a more typical estuary with a huge expanse of water when the tide is in and mud flats when the tide is out. His house is 250m from the water but flat terrain.

    So my brief is:
    1. Most likely skin on frame - It needs to be lightweight so it can easily car top and wheel up/down a hill to the water. I'm thinking of a wheeled dolley that I sling underneath just like SIBs pulled up the beach. Something as light as a SOF could also be stored in the garden/parking area of a holiday rental cottage.
    2. Flat-ish bottom for landing on a beach and good stability for ferrying 3 people across the estuary with a small outboard - just like a SIB.
    3. Sharp bow and V bottom for good sailing in choppy estuary waters, which is why I haven't simply gone out and bought a SIB!


    So far I'm thinking of adapting an established plan for SOF techniques with a ply bottom.

    These seem like good candidates:


    As I see it, I have a trade off between a good sailor and a flat bottomed plodder good for the ferry duties. I do like the look of the Highlander 10, while the Monfort Cartopper needs no adaptation for SOF. So many choices!!! ....
    A very interesting idea the ply bottomed SOF and though some have been designed and built when I looked at designing one it became a route of diminishing returns. As the bottom panel increases in size to a practical width the weight goes up. I concluded that a Mirror Dinghy at 45kg had more merit.

    http://forum.woodenboat.com/showthre...t-Rad-SOF-pram

    I must point out out though I have never built a SOF boat and this was just a thought experiment based on what information on scantlings I could find on the net

    When I get time I would like to model up a design based roughly on the Mirror but stripped down - stitch and glue ply - and see how light I could get that.

  3. #3
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    Default Re: SOF estuary dinghy

    The CLC Passagemaker, even in ply is not that heavy, and can also be made as a 2-part dinghy. I have gone down the route of thinking of ply bottom and skin sides, but as Tink points out, its a balancing act. If you want a load carrier and use an outboard, the Passagemaker would be at the top of my list, a SOF version, by the time it has been made stiff enough to perform may not be that much lighter.

  4. #4
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    Default Re: SOF estuary dinghy

    Dave Gentry http://gentrycustomboats.com/ mentioned something about a SOF square sterned canoe. Don't see plans out yet. Square sterned canoes are brilliant small motorboats. Adding sailing to the mix might not work well.

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    Default Re: SOF estuary dinghy

    If you get yourself a copy of Traditional Boats of Ireland, there is a lot of information on "skin boats". Probably the best recourse of information i have come across on the broad spectrum of skin boats and types built in Eire, i think they could have made a good book from that large chapter alone.

  6. #6
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    Default Re: SOF estuary dinghy

    Dave Gentry Annabelle 10' 29kg
    Clint Chase Echo Bay Dory Skiff 11' 7" 38kg, - ply solid chine

    http://www.chase-small-craft.com/sailing-echo-bay-dory/

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    Default Re: SOF estuary dinghy


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    Default Re: SOF estuary dinghy

    Aha! I knew in the back of my mind there was a boat for the job, a chat with a seafaring Cornish uncle reminded me of the Yorkshire Cobles. They were working boats for launching off a beach in the rough North Sea to bring in the catch from fishing boats. Hence perfectly suited to the choppy waters at Salcombe (onshore wind with ebb tide can get very choppy!), plus stable platform to act as a ferry. Plus a stable base to introduce young children to sailing on the more placcid waters of the Exe.

    Selway Fisher have an all wood 10ft coble weighing in at 34kg http://www.selway-fisher.com/Cobles.htm#NOR

    That's just 5kg more than Annabelle, so the SOF doesn't save much weight. If I did go for a GA style SOF (ie a classic)) I'd end up putting wood back in for a floor, thawts ( my ferry passengers expect a seat!) and mast seat and a bulkhead at the mast, oh a dagger board box too. Hence the weight will creep back up.

    I think I'll go for an all wood coble.

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    Default Re: SOF estuary dinghy

    Sounds like a pretty sound decision to me, keep us posted.

  10. #10
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    Default Re: SOF estuary dinghy

    I do wonder about the specified weight of that Coble design. A Mirror dinghy is about the same dimensions, is built from 4mm gaboon plywood and without oars or rig weighs 45.5 kg. This boat is built from 50% thicker plywood and is 25% lighter. I think you would at least need to be pretty careful about not using too much epoxy to stick it together.

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    Default Re: SOF estuary dinghy

    Quote Originally Posted by John Perry View Post
    I do wonder about the specified weight of that Coble design. A Mirror dinghy is about the same dimensions, is built from 4mm gaboon plywood and without oars or rig weighs 45.5 kg. This boat is built from 50% thicker plywood and is 25% lighter. I think you would at least need to be pretty careful about not using too much epoxy to stick it together.
    The Mirror was built with 3/16 ply 4.76mm, as this is not available anymore they are now build of 5mm ply. The original 45.5kg weight was based using polyester resin and I suspect chopped stand mat. The Mirror has a lot of internal joinery work all of which makes the 45.5kg a remarkable achievement by Jack Holt.

    The Coble has much less internal work and the benefits on Epoxy and wowed tape, 34kg is however impressive but expected range




    LOA ft
    Weight Lb
    Lb / ft
    PD
    8
    120
    15.0
    Mirror
    10.8
    100
    9.3
    GIS
    15.6
    128
    8.2
    Streaker
    12.8
    106
    8.3
    Coble
    10.5
    75
    7.1


  12. #12
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    Default Re: SOF estuary dinghy

    What kind of outboard would you use on a SOF?

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    Default Re: SOF estuary dinghy

    Good choice. A simple rowing boat is simple and light in SOF. When it comes to adding floors, casings and semi-bulkheads for mast pressures, weights do add up......another reason i have not yet committed myself.

  14. #14
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    Default

    Quote Originally Posted by Salcombe View Post
    Aha! I knew in the back of my mind there was a boat for the job, a chat with a seafaring Cornish uncle reminded me of the Yorkshire Cobles. They were working boats for launching off a beach in the rough North Sea to bring in the catch from fishing boats. Hence perfectly suited to the choppy waters at Salcombe (onshore wind with ebb tide can get very choppy!), plus stable platform to act as a ferry. Plus a stable base to introduce young children to sailing on the more placcid waters of the Exe.

    Selway Fisher have an all wood 10ft coble weighing in at 34kg http://www.selway-fisher.com/Cobles.htm#NOR

    That's just 5kg more than Annabelle, so the SOF doesn't save much weight. If I did go for a GA style SOF (ie a classic)) I'd end up putting wood back in for a floor, thawts ( my ferry passengers expect a seat!) and mast seat and a bulkhead at the mast, oh a dagger board box too. Hence the weight will creep back up.

    I think I'll go for an all wood coble.


    Some real and Model Cobles from Hartlepool Museum. Perhaps yours should be a Corf. Plenty of Cobles the other side of the Tees at Redcar, all sadly with motors in them but still very much used.



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    Part 2


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    Part 3


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  17. #17
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    Default Re: SOF estuary dinghy

    The best and classiest boat you could build would be a traditional carvel built Falmouth Punt. Displacement low hp motor, oar and downwind sail, though i've seen one with foils. This won't be light and would take a few years...but that's your traditional west country estuary oystering, ferry and work boat type. The only lines are available from Paul Gartdide. To save time you could fit out a £800 Cygnus 15 grp hull which was molded off an old one, local oystermen would still respect the choice.





    Alternatively, you could stitch and glue together some plywood, and you want car top light..





    I'll suggest Lillistone's Flint, for a motor, sail a row boat car topper. The hull weighs 35kg and is 15ft long which will give you space for 3 and speeds of 6-7 knots under half throttle using a 2hp with 4 aboard. 70 hrs of work and a shallow V bottom, narrow entry, higher length to beam ratio, car tops and goes over hull speed under power. That boat will give you alot of utility for the time and weight / cost of materials invested. Not having the flat planing aft sections of Fleet gives you the row capacity and Flint has a few sailing rig choices. Its superficially a simple boat, but one that has been deftly and carefully designed.

    Last edited by Edward Pearson; 07-28-2017 at 04:18 PM.

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    Default Re: SOF estuary dinghy

    Thanks Edward. I was on the Exe today and as well as the Falmouth punts the are a few Devon yawls too, a couple moored next to the Topsham Ferry. Here's a stock photo from Salcombe although they are rare there, I see more of these on the Exe.



    The dominant local boat typology in Salcombe seems to be a Zodiac, they're an inescapable buzzing swarm. Just about every boat in the pic below is a RIB or SIB...



    To be serious , I did have a look at the Flint and thanks for highlighting it. It does give a lot of feet per kg. If was just me then I'd go straight to something like that.

    However, a stable ferry ( that I can happen to sail or row) is the prime objective in this case. The zodiac inflatables in Salcombe tend to stop in a foot of water to avoid the outboard grounding, tilt the outboard up, one person jumps out and pulls the boat until the hull grounds and then the remaining passenger paddle ashore. The boat is then pulled clear of the waves.



    My objective is to replicate that for landlubber passengers, picnic cool boxes and children's beach clutter. I've seen Mirrors do that but they do look unsteady in the transition from shore to floating. Someone has to hold the boat upright while the passengers get in and out.


    So why don't I get a Zodiac? Well I would also like to mess about with oars and a sail but zodiacs are rubbish for that! Also a boat that only plods would be useful to introduce my young daughter to sailing - albeit on the Exe which is like a giant millpond when the tide is in.

    I must confess that I do like the wallowing lines of the cobles, but agree that just about every cove in Devon and Cornwall has a few Falmouth punts bobbing about on the water or pulled up on the beach in places like the Lizard. What would you say the boat is on the right in the pic of Lizard Point below? That seems suitably tubby for my needs.


  19. #19
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    Default Re: SOF estuary dinghy

    Thanks for the pics Tink. Perhaps a Corfe would be a more appropriate term.

    One of those pics had a distinctly pointy stern which seems most unike the cobles. The description on this link refers to the corfe or calf had having a nipped stern. http://yorkshirecoastmaritimearchive.co.uk/?cat=29

    That site has fascinating descriptions of how these boats were used.
    Last edited by Salcombe; 07-28-2017 at 07:28 PM.

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    Default Re: SOF estuary dinghy

    Quote Originally Posted by Salcombe View Post
    Thanks for the pics Tink. Perhaps a Corfe would be a more appropriate term.

    One of those pics had a distinctly pointy stern which seems most unike the cobles. The description on this link refers to the corfe or calf had having a nipped stern. http://yorkshirecoastmaritimearchive.co.uk/?cat=29

    That site has fascinating descriptions of how these boats were used.
    The one with pointy stern was a Pilot boat, so speed rather than load carrying would be the order of the day. I also imagine that it would not be kept on the beach but in the harbour. Thanks for the link will full read tonight.

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    Default Re: SOF estuary dinghy

    If you want 'more boat' than Flint, its going to start weighing more and you will be looking at trolley/ trailers. Typically hull weight will creep to 50-100kg for a sailing tender to dinghy of conventional form.

    I'd look at Oughtred's Auk. Can be built at 9ft. Its a burdensome hull, of west country type, nice rig. It will be a bit of a squeeze if you always have 3 in it. Looked over an 8ft one at Lyme. I'd sail an Auk accross the Channel with buoyancy tanks and expect to make it.



    Another good sailing tender would be John Welsfords Sherpa. Its flat bottom panel will mean it doesnt rock when on the sand like a shallow V mirror. It also saves some work. I've only seen a Tender Behind, but i'd expect it to be the most robust and burdensome sailing tender you could possibly find. There's video of one going well in the Texas 200 in some wind. A few people have put a slightly bigger sail on it.



    D.Hylan designed Oonah as a RIB alternative. Worth a look.



    Wolstenholme's Coot's are very good. We've had two over the years. Under sail very fast in light air, but more boat again.




    Regarding Flint, its no narrower than these sailing tenders but longer. Stability can be gained with waterplane length, not just beam. It also improves the boats speed potential. Also as you reduce the entry and exit angles you get more laminar flow. One effect of that can be a drier ride.

  22. #22
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    Default Re: SOF estuary dinghy

    Flint or Fleet are a perfect example of how a well designed plywood boat can end up being as light as a SOF, you get the advantage of using the ply skin as a stressed member, where with SOF you have to add stringers and frames, its surprising how it adds up.
    If easy beach landings and loading from the beach are a concern, how about a large pram or garvey type? One of the better ones for weight Vs load capability is Paul Fishers Harrier


    Designed for cartopping, but pushing it at 66kg, and EU roof bars are going to need extensions. Not quite the right hull shape for sailing though, but his Skylark 10 dinghy at almost half the weight, would be just as practical.



    Forum member John Hartman built an extended Herroshoff pram in SOF, you might find a thread on it.

  23. #23
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    Default



    SOF can be lighter depending on what materials you use. Here's a Merrymeeting Bay Duck Boat from Gardners lines in Classic Small Craft, about 15'x4'. I think I saw a planked, all wood build weight somewhere in the 200-250lb range. Mine comes in at about 130lbs and is just barely car-top-able alone, but I prefer help. It think it could have been built lighter and just as tough but I over built it because of it being used in hard conditions.

    Things I'd try differently is use a lighter weight (8oz) polyester with a PL premium bottom rather than the 12-14oz nylon with 2 part urethane. Boil bend white oak ribs and hand pick the lightest weight, clear white pine planks I could find for the stringers. Also would use lashings instead of screws. That should save a bit of weight on both the skin and frame and I think that would get it down to about 100lbs, maybe less. And there tougher than you think and you shouldn't have any problem with a small engine as long as you stay within the designed performance of the hull (don't as a displacement hull to plane). I'd put a 2-3hp on my boat any day without a 2nd thought.




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  24. #24
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    Default Re: SOF estuary dinghy

    That Coot is gorgeous, but a fully fledged boat at 104 kg for 11'.

    I do also like the Auk, but now I've seen the Puffin at 45kg for 10'. I wonder if some designers include the sail rig in their weight and others are hull only? The Puffin is beautiful and I'm thinking it's a bit more boat that the Selway Coble, but the benefit would be worth the extra weight? It's top end of my weight criteria, I've used a 40kg canoe for dragging up the street from the water, as well as onto the car and decided that was my limit. I suspect the Puffin will require a lot more time too ....



    Dalton - Interesting fenders, are the feathers to avoid scuffing the mother ship?

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    Default Re: SOF estuary dinghy

    Stated weights vary wildly among designs, some few are accurate for the complete, painted hull, others more fully outfitted, still more just a rough estimate from the designer, and finally some list the displacement for the weight and are therefore really high. Numbers on 3rd-party plans lists like WB Store and Duckworks sprinkle all of these weights togethe under one headingr.
    The most reliable numbers I've found are builder's weights from this forum, or designers who currently build boats themselves, like Gartside or Welsford. If you're lucky a pro boatbuilder who advertises the boat. At least I would confirm what stated numbers represent with the designer.

    Cherrs, Dan

  26. #26
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    Default Re: SOF estuary dinghy

    Since you mention Platt Monfort's Cartopper, I thought I'd chip in with my experience with a Platt Monfort Classic 12. It weighed nothing (I can't remember exactly, site claims 30lbs) and was a exceptionally nice sailing and rowing boat. So, you might do well with the one next size up, the Classic 14. I would replace the dacron he specs with ballistic nylon....

    Your description seems to be calling for a few contradictory things--stable platform that doesn't have to be steadied as people load (so, a big, fat RIB...) but with a sharp bow for choppy conditions. So, no prams, though the "sharp bow" is no panacea. Prams can be pretty good in sharp chop. I was going to suggest a Mirror but you vetoed that one. It would seem almost ideal (and they're all over the place Over There). Anyway, the Classic 12 was a heckuva boat, and I think the 14 would be not only an effortless cartopper, but a great sailor and capacious, to boot. Easy build, too. They're fairly flat on the bottom and not especially tiddly, as per this copy from the site, re the 14 vs. the 12:

    "The main difference is the reduced deadrise on the bottom which was done to compensate for the ultra light weight of the Geodesic AiroLITE® boats"

    48 1/2" beam vs 52 1/2" the Cartopper but on an extra 5 feet of length. The 12 was surprisingly roomy.



  27. #27
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    Default Re: SOF estuary dinghy

    Just following...

    Any idea when you are going to start the build? (Is it start building/start the built?)

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