How Do I Design a 3' Draft Boat to Be Seaworthy ?

[David_Old_Jersey]

Not entirely familiar with Thames - but you sound a long way up. Therefore I suspect you won't be making day trips down to the sea (and back), and maybe not even for the weekend? Therefore Norfolk broads style ease of mast dropping not so important - drop the mast once and raise it upon arrival. Nonetheless being able to drop the mast without a crane would be useful. A tabernacle can be a retrofit, but it all costs.

But given your budget I think going for older GRP is the route to go, and settling on cross channel or north sea capable rather than RTW (don't thik that those areas are easier than oceans just because nearer - just different challenges, some easier, some much harder). RTW capable is for the next boat once you learn what is important to you.......and anything from Boatman's suggestions would be capable of taking you along your own learning curve - whether you would then be able to (or would then want to) is a seperate issue.

Designing your own boat? keep it in your head, and use your design thoughts to influence your choices of other people's designs.

[Thames]

I agree with you all, if I design a boat it will be purely for fun, with no benefits in cost or final outcome. She certainly won't match a production boat. For some reason building someone else's design doesn't appeal so much - it's almost like somebody ate the insides of a Cornish pastie before they gave it to me - it's the creative part I'm after.

I may well end up buying production GRP, but I will have learnt so much from this discussion that I will better understand what I need and what compromises I have to make. Thank you all for your valuable contributions to this thread.

The Virgo Voyager looks good to - I suppose with a shallow draft boat, it's a compromise between headroom and windward performance. Here's one for £4500 ready to sail. And here's a different one:

So how easy is it to retrofit a tabernacle? I'm assuming the boom has to hinge as well? I would like to be able to raise and lower easily but perhaps only on the longer open stretches of the Thames where bridges are more than 3 miles apart. In London at mid-tide the dinghies clear the bridges, but I don't think a small yacht would until low tide. Further up river no chance.

[Mark Johnson]

Weyalan... I couldn't have said it better myself!

I have built all three of my cruising multihulls, (taking 21 years of construction all together). If built carefully and according to well proven plans, one knows what they will end up with in almost every respect. They have a track record.

To design a boat yourself, is to spend years of your life and countless thousands of $ (or pounds) building it, only to end up with in an unknown result. This, to save about $500 for some "stock" plans... is insane! DON'T DO IT!

Take a look at the Wharrams or better yet a Searunner 25. With cruising skill, that is about as small a Multihull as I would go to sea in. My first project was a Wharram 23, and while seaworthy, it was brutally spartan!

Good luck, Mark

[boatman61]

Well worth a read.... amateurism at its boldest and best... it helped open my eyes to boats and what they need and what many TELL YOU they need.... not always the same....

[Thames]

Thanks for the encouragement boatman! Just ordered that book too. So I can learn how to get naked ladies to ride my bow

Phew this forum's expensive...that's gotta be £100 on books by now! They're all out of print too.

I see a tabernacle on your Hurley 22 - was that difficult? What did you do to the boom and the forestay?

[Mark Johnson]

Thames,
Good book to get your juices flowing... We visited Scotland this summer, and I saw the advantage / necessity in your area, of shallow draft and the ability to spend much of the time sitting on the bottom. For this, the Wharram would be even better than our beloved Searunner tri. You are young and energetic. Perhaps this level of camp / cruising would be up your alley? His newer designs offer "deck pods", (in the larger ones). This gives a dry spot to stand watch, which was sorely missed in mine!

These are incredibly simple, basic, easy to build boats. They aren't windward screamers, but MUCH better than a bilge keel mono. Off the wind, they really sail... although, with a bit of leeway. The accommodations are so small, and they are so minimalistic to build, that I wouldn't go with smaller than about 30' long, if you want to live on and cruise the boat. With a thickly glassed keel, they are as "bottom friendly" as a boat can be! Wharram, being a fellow Britt, would presumably be available to consult as wall as sell you the plans. AND he promises that your boat will be crewed with not one but SEVERAL naked women! How can you beat that!

A tabernacle mast is not a problem. Of coarse you need a hinge base... You rig some side shrouds with a bit of stretch to them. Hook up the forestay as well. Then you also rig some stretchy lines from the boom end to keep it under control. It needs a strong toppin lift line to the mast head. (this makes the boom a "gin pole") With a block & tackle you can raise the mast by pulling aft and down on the boom end. It is really easy once you get your "system" figured out. You can do it by yourself.

Good luck! Mark

[boatman61]

A lot of Hurleys were fitted with tabernacles to facilitate trailer sailing... they're pretty simple set-ups.. a base plate with an 12 - 18in cheek either side, a back plate about 6in and the front open... two holes for through pins to hold the mast upright till you set the stays... pull the bottom pin for lowering and the mast pivots on the upper pin... forestay is released and a line attached for lowering.
My boom could hinge up flush to the mast...
My Avatar is now my former Tiki 21

[Thames]

Thanks will definitely consider the catamaran, although I'm not sure how popular the increased beam will be on the upper Thames. I reckon the Warram book will be a good read regardless.

About the Hurely's tabernacle I'm assuming this is difficult to do underway? You'd have to walk forward to take the pin out. I'd love to be able to do what the old Thames Barges did - lower the mast while still sailing, shoot the bridge without loosing momentum and raise it again sail and all. Anyone know how?

And do all these changes compromise the overall strength of the rig?

[boatman61]

LOL... yeah... get a crew of three plus you... also you've got to remember something else about Thames Barges... they come up and go down river using the tides... thats how they maintain the momentum... you'll never see one coming up against unless its also using the engine..
Seriously if the bridges are only 3 to 5 miles apart leave it down and motor.... you'll need a X frame at the stern to rest it on as well...
The book is meant to inspire possible design ambitions... JW was not a 'Designer' back then.. just someone with an ambition/dream, found inspiration from traditional native craft which 'Logic'd into his first cat...
And what changes... if you mean the tabernacle... no.. if anything it makes the mast foot stronger.
PS; The cat is not for the Thames... just me showing off.....

[Thames]

Thanks boatman, that's very encouraging - you're the first person who hasn't just told me to stick to piano repair!

I've been asking about leeboards or bilge keels because I'm afraid of complicating design by making holes in the hull, but people have suggested that making the cases for centreboards and the like is really not that difficult, and that with modern epoxy leaks aren't an issue. Is this true?

If so a ballasted swing or lifting keel sounds very attractive, if it could come up flush with the hull to allow beaching. Swinging the ballast down 8' below would be fantastic for offshore stability. Lifting keels scare me a bit if I were to go aground. But a swing keel would just fold up - what do people think of swing keels?

[boatman61]

Originally Posted by Thames

Thanks boatman, that's very encouraging - you're the first person who hasn't just told me to stick to piano repair!

I've been asking about leeboards or bilge keels because I'm afraid of complicating design by making holes in the hull, but people have suggested that making the cases for centreboards and the like is really not that difficult, and that with modern epoxy leaks aren't an issue. Is this true?

If so a ballasted swing or lifting keel sounds very attractive, if it could come up flush with the hull to allow beaching. Swinging the ballast down 8' below would be fantastic for offshore stability. Lifting keels scare me a bit if I were to go aground. But a swing keel would just fold up - what do people think of swing keels?

Epoxy is great stuff... it allows you to not be so exact with your joinery... just fill the voids with a nice gooey epoxy n micro fibre mix... job done.
The one thing you got to watch though is cleaning and preping after each application... when curing epoxy forms a waxy coat on the surface which needs cleaning of well with acetone, then washed with fresh water and sanded for a key before the next application.
Swing keel... lifting keel are just different names for the same thing... also most have the ballst in the bottom of the boats hull itself... the actual keel forms only a small portion of the total... its for directional stability not boat stability... unless its a stub keel for shoal draught work and the swing for deeper water.
Piano repairs not so bad if it pays the bills for the boat...lol

[bljones]

6'2" headroom is gonna be tough on a small boat, unless you opt for something with a poptop. One of the reasons we bought our Georgian was the headroom. It has the tallest cabin of anything under 25', but with that being said, it is still only 6'1".
Check out some of the smaller Westerly twin keelers. I think the Westerly Pageant offers decent headroom in a small package.

Westerly Pageant yacht designed by Laurent Giles. Information and advice on sailing and cruising

[Thames]

Well I think piano tuning's great for living on a boat - no heavy tools, no fixed schedule, pianos all the way up and down the Thames and hopefully in some exotic ports of call too!

Way too expensive, but here's my ideal boat, it has a swing keel: Southerly 32 (requires Flash Player and you might need to refresh page)

Please correct me but I assume a ballasted swing keel swings out forward on a pivot when pointing high but swings back aft and flush with the hull for running or shoals like this:

..whereas the lifting keel lifts vertically straight up into the hull like this:

But perhaps I've got the names wrong. So if the lifting keel grounds at speed it could break off but the swing keel would just swing back. And when up the swing keel will bring more weight aft which should help her when running, no?

Obviously This will take a lot more careful design and construction, but perhaps worth it for the best of both worlds offshore and 'gunkholing.' Or do you know of any cheap secondhand production swing keel boats? They have been used since 1980.

[bljones]

If you're looking at a boat that you can run up on the beach to explore the wild shores of the untamed upper thames, you might want to rethink your plan. Go outside and try to pull your car 20 feet. Tough, innit?
now take the wheels off and try it again.
Now take the wheels off and try it again, in the mud.
Now take the wheels off and try it again, in the mud, with four of your best mates in the car.
Now you're close to the weight of a reasonably serious 20-25' boat.
At which point did you pass out?
So let's set aside the idea of beaching the mothership, and play D and D:
Davits and Dinghy. Take your gunkholer with you wherever you travel, anchor where the water is not thin, and dinghy into where it is. A smaller vessel would also allow you to visit places you could never fit the mama ship into.

Personally, i don't like swing keels- If you wish to venture far and wide, stay simple- the fewer moving parts, the better.

[boatman61]

Originally Posted by Thames

Well I think piano tuning's great for living on a boat - no heavy tools, no fixed schedule, pianos all the way up and down the Thames and hopefully in some exotic ports of call too!

Way too expensive, but here's my ideal boat, it has a swing keel: Southerly 32 (requires Flash Player and you might need to refresh page)

Please correct me but I assume a ballasted swing keel swings out forward on a pivot when pointing high but swings back aft and flush with the hull for running or shoals like this:

..whereas the lifting keel lifts vertically straight up into the hull like this:

But perhaps I've got the names wrong. So if the lifting keel grounds at speed it could break off but the swing keel would just swing back. And when up the swing keel will bring more weight aft which should help her when running, no?

Obviously This will take a lot more careful design and construction, but perhaps worth it for the best of both worlds offshore and 'gunkholing.' Or do you know of any cheap secondhand production swing keel boats? They have been used since 1980.

LOL... Opps... sorry about that... the only boat I've seen the 2nd example on was a 17metre Jungert which had everything push button hydraulics.. including the sheet winches... the cockpit position rivaled the Starship Enterprise....
The average/majority small boat is the former... as I said... ballast in the hull... not the keel.. these keels are winched up by hand in the cabin...
Take a look at the Seal 22... they are lift keelers from the late 69 onwards... the only one of its type/size made in the UK.
Seal 22 archive details - Yachtsnet Ltd. online UK yacht brokers - yacht brokerage and boat sales