Bilge keel performance design

[flaming]

My Dad's first boat was a twin keeled Griffon. We simply never visited drying harbours, so it's replacement was a fin (though a shallow draft option). I think we dried it out once, and that was not intentional, it was a navigational error....

The reason so few visit drying harbours is simple really. Time. If you're still working you have to fit your sailing in on weekends, or your precious annual leave. To then visit a tidally accessed creek and hole up for 12 hours may well seem to many not the best use of that scarce resource - time.

And that's before you ask whether someone bought a boat because they like sailing, or because they like sitting on it in interesting places....

 

[bbg]

@dancrane

Do you have any idea how condescending you sound?

Wake up. You are out of step with what most people want. If there was a demand for twin keel boats they would be built. Your idealized, romanticized notion of the kind of sailing you think you would like to do is not what most people want to do. Or at least not a high enough priority to make any difference to their choice of boat.

 

[lw395]

....

The reason so few visit drying harbours is simple really. Time. If you're still working you have to fit your sailing in on weekends, or your precious annual leave. To then visit a tidally accessed creek and hole up for 12 hours may well seem to many not the best use of that scarce resource - time.

And that's before you ask whether someone bought a boat because they like sailing, or because they like sitting on it in interesting places....

It's also a case of restricting your options.
There are some nice places in Brittany etc where you can dry out, but if you can only leave at high tide, the tide outside is only going one way (e.g. West) and you won't be arriving at the next place at HW unless it's very close or many hours away.
I've known a few people with twin keelers who rarely ground them.

 

[flaming]

It's also a case of restricting your options.
There are some nice places in Brittany etc where you can dry out, but if you can only leave at high tide, the tide outside is only going one way (e.g. West) and you won't be arriving at the next place at HW unless it's very close or many hours away.
I've known a few people with twin keelers who rarely ground them.

Very true, same issue with the marinas behind cills in that part of the world. Leave as soon as you can scrape out over the cill, along with half the marina, and clock watch all the way to the next highly tidal marina, where you arrive in the same bunch. Sometimes felt like an informal flotilla!

 

[DJE]

My Dad's first boat was a twin keeled Griffon. We simply never visited drying harbours, so it's replacement was a fin (though a shallow draft option). I think we dried it out once, and that was not intentional, it was a navigational error....

The reason so few visit drying harbours is simple really. Time. If you're still working you have to fit your sailing in on weekends, or your precious annual leave. To then visit a tidally accessed creek and hole up for 12 hours may well seem to many not the best use of that scarce resource - time.

And that's before you ask whether someone bought a boat because they like sailing, or because they like sitting on it in interesting places....

We dried out our twin keel Sadler 29 fairly regularly in the 15 years that we had her. But generally only in places we knew. Drying out on an unknown bottom was always a nervy experience and if you add a visit in the dinghy at low tide to check the bottom then your 12 hours becomes 18. And most quay walls have a bed that slopes away from the wall making them more suitable for single keels than twins.

This exploration of drying creeks isn't as idylic as you might think!

 

[Lucky Duck]

Having grown up on boats kept on drying moorings we started off in a 'twin fin' Hunter which we also kept on a drying swinging mooring as a berth at a marina wasn't really affordable at that time. After a couple of years we moved into a marina and shortly afterwards swapped the Hunter for a fin keel Beneteau First and haven't really looked back.

Even on the East Coast there were only a few places denied to us and I suspect my current boat's size would also prevent us visiting if we did had twin keels.

However one thing I do miss is being able to beach for a scrub or to check on the anodes without having to wait out a full tide when on scrubbing piles

Looking at the photo in the OP I imagine the height difference between the pontoon and the boat at low water must make life interesting and requires some skill in arranging the lines so it doesn't drift off too much when the tide returns.

 

[TSB240]

Looking at the photo in the OP I imagine the height difference between the pontoon and the boat at low water must make life interesting and requires some skill in arranging the lines so it doesn't drift off too much when the tide returns.

You are so right. We were moored up close to one of these in Sauzon Harbour. They towered over the top of us and the biggest problem was that when we refloated we had to prevent ourselves from going under their hullside with our kedge over the opposite side....

 

[laika]

Sorry to step into a discussion on the racing forum when my contribution is about to be non-racey.

dancrane may be in a minority but it's not a minority of 1. I bought a 12m long fin boat for a long distance deep water trip I've not yet set off on. After a couple of years I realised that had I known I was going to stay in the UK what I would have wanted was something 9-10m, which performed well to windward (I don't want to round-the-cans it but I like to be able to travel reasonable distances in a reasonable time) and most importantly could take the ground so that I could explore more of our beautiful coastline. Draft *isn't* the issue. I like the technical aspect of playing the tides. Once I get somewhere though I like to stay the night and have a beer. Plus you have more options in popular anchorages which dry round the edges.

I see the argument that anyone wanting a twin keeler for economy of mooring will probably not be buying new. After having looked at Legends a couple of years ago I'll also question why anyone would spend the money on a new boat with an interior which looks like it's made from cardboard and balsa. If I'm buying new I don't want something which feels more cheap and nasty than a 25 year old Fulmar and doesn't perform as well.

The French boats linked to look interesting (thanks for that) but not very..well...cosy inside. Would there be a market for a twin keeler closer to (though not quite..) halberg rassey 310 quality, but with twin keels? Were I to be convinced back to a "proper" career in the UK for a while, I'd be a potential customer.

I'm guessing creek crawling is a minority pastime for a number of reasons. Partly because it's a little more challenging to some than marina hopping. Partly because "party ashore" is some people's expectations for a weekend sailing. Mainly because people mostly buy fin keels. Why? Maybe there's not a range of twin keel options available, maybe because the perceived performance penalty to windward, maybe because BenJenBav have such great economies of scale in the med charter markets that their fin keelers offer such excellent value, maybe because a lot of people buying mass market boats buy what they're familiar with from what they've sailed on charter and at sea schools, maybe because first time boat owners don't realise why they need a twin keel boat until they've bought a fin keel and realise how it limits them...

Shame HR, Najad etc. are from a country with deep fjords...

 

[DJE]

I own a good twin keel boat, a Sadler 290, from new since 2004.

The one thing I didn't like about the twin keeler Sadler 29 (apart from being a bit small) was that when hard pressed the root of the windward keel would break the surface and she would slam. Do the 290s or the modern French twin keel boats do that?

 

[Tranona]

Would there be a market for a twin keeler closer to (though not quite..) halberg rassey 310 quality, but with twin keels? Were I to be convinced back to a "proper" career in the UK for a while, I'd be a potential customer.

You could buy a Sirius in sizes from 31-40' with twin keels, but you might find the prices make an HR 310 seem cheap!

The Sadler 290 is(was) very close to what you describe and was quite popular, selling, I think about 60 boats before they realised the price they could get did not yield a profit. there was a 34/5 in the pipeline also with twin keels but never made it to production.

Still not convinced there is a market - the twin keel Westerlys and Moodys died a quick death in the 1990s when they started fitting efficient fins.

 

[Greenheart]

The reason so few visit drying harbours is simple really. Time. If you're still working you have to fit your sailing in on weekends, or your precious annual leave.

I reckon you're right. I expect most new-boat buyers are still mostly working when they'd rather be sailing...so however enticing drying harbours might be on occasion, there isn't time on a weekend to just sit aground. And keeping a yacht in a marina means no time lost, getting aboard and sailing away...and when a longer period is available, a more ambitious destination is a natural choice.

Work...shudder! Frightful business. I'm suddenly glad I do so little.

Nice pic, I thought.

 

[Habebty]

The one thing I didn't like about the twin keeler Sadler 29 (apart from being a bit small) was that when hard pressed the root of the windward keel would break the surface and she would slam. Do the 290s or the modern French twin keel boats do that?

No they don't slam, but as in the French example shown in the op, drying out next to a pontoon can indeed be interesting, I have a similar picture of my boat in Wells next the sea at low water which meant a bit of stretch to get on and off
I think Dancranes picture might be in Norfolk as well?
I would have loved a Sadler 340! Which looks very similar to the GT35 funnily enough.

 

[Birdseye]

The market for twin keel boats would pick up here if people realised, like the French, that performance need not be compromised by having an extra keel. With a good designer, why have just one keel when you can have two?

View attachment 54020

Sadly thats simply not correct. The lift provided by a foil depends , amongst other factors, on the ratio of chord to length. Have a read of http://www.sponbergyachtdesign.com/keel and rudder design.pdf which explains what is happening. Sure you can have very good bilge keels and very good deep fins but the deep fins will always work that bit better. Which is what you would expect - after all when did you see a seriously expensive racing boat like the monohull americas cup boats using twin keels?

 

[Greenheart]

...when did you see a seriously expensive racing boat like the monohull americas cup boats using twin keels?

I've no idea...I believe I'll be quite happy with an old Solway or Pentland ketch when I finally shop for a yacht...

...but while I don't like the way this thing looks, I bet it's much quicker than the vast majority of fin-keelers which are confounded by drying harbours...

 

[Boo2]

Anyone care to enlighten me as to what boat that is ?

Thanks,

Boo2

 

[Greenheart]

Sorry Boo, no idea. I just Googled 'twin keels' and clicked "images". You may find what it is if you go to the associated page when you find the picture among the many there.

 

[AliM]

Transona mentioned Sirius's. They started making twin keel boats with the 310DS just 5 years ago, and the designer used some modelling in Hamburg University to optimise the design for sailing performance. Germans were very sceptical about the performance of twin keels at the time, and the designer was no exception. He told us that they could not be expected to perform as well as fins and he could not see why anyone would choose twin keels. That was when we did a test of our new twin keeled Sirius 310 against an equally new fin keeled version, in the Baltic in May four years ago. The designer sailed on the twin keeler in the morning and the fin keeler in the afternoon, and petty well all the employees from the boat yard were there on other boats. The twin keeled boat sailed as well, or better, than the fin keeler in every way on all points of sail. Everyone, not least the designer, was pleasantly surprised. Since then, they have done similar tests on the 35 and 40 FT Sirius's with the same result. And since then about 60-70% of the boats they have built have had twin keels. Note that these boats are designed to have excellent sailing performance - not out and out racers, of course, but they are certainly not in the sailing caravan class!

 

[Birdseye]

Better get in touch with Knox Johnson then . If he were to put bilge keels on his race boat he would obviously win rather than come third.

 

[Daydream believer]

(Note that the "cutting off" of the track on a couple of the tacks is an artefact of the track logger not logging a position near enough to the time of the tack)

We were beating into the Blackwater with a fair tide of a knot or so, give or take (we crossed the Spitway at nigh on low water IIRC) with two reefs in the main, a big chunk of genoa rolled away and 25 to 28 knots of wind in our teeth. It was quite, erm, lively out there as well!


Now tell me "bilge" keelers can't sail to windward!

taking into account the tide there is nothing startling about that. 45 deg to the wind. ie 90 degree tacks
Without the tide that would have been much more
Pants really.

 

[Daydream believer]

Interesting thread, thanks for contributions. The following isn't meant to rile anybody, it's just what seems to me to be the way things are, despite publicity-people's deceptive ways.

Mr Tranona has explained to me why almost all the boats I'd like, aren't built...some of the reasoning is excellent, though what it says for new-boat buyers in the UK, isn't flattering.

I can certainly see that anyone buying a costly new yacht is very unlikely to want to leave her on an inexpensive drying mooring...and of course, the manufacturer has no reason to cater for the convenience or economies of his products' third/fourth-hand owners, long after the factory-sheen has worn off, and a large proportion of her initial value too...

...so, long after the ageing fin-keeler's owner wishes he could berth her annually for a small proportion of what he paid for her, her design still requires a pricey deep-water mooring.

That seems unarguable because it's inevitable, if a bit sad, like all those once-grand cars whose resale value today is tiny compared with the cost of any repair to the bodywork, though perhaps it permits low-budget folk to own for a while, some faded, almost-glamorous things. But...

...the reasoning overlooks a basic line of thinking (not exclusively my own, I hope?) which is that in the UK, it is appealing to be able to visit drying harbours, rivers, beaches, etc...

...and the default solution, those delightfully versatile lifting-keel boats, are on close analysis mostly too vulnerable to rocks, wrecks and mooring blocks, to actually leave to dry.

So we have to assume that all new-boat buyers decide like sheep, that they'd much rather be herded into marinas and limited deep-water space, and that they'll cheerfully sign the cheque, acknowledging that all those sheltered shallow blue bays and idyllically peaceful wooded drying creeks are going to be permanently out-of-bounds to their new yacht...

...but surely that isn't the case? I reckon it's generally acknowledged here, that a laughable number of offshore yachts never go offshore...most of their owners are pressed for time, so whatever their ocean-going dreams, they rarely go further than attractive accessible local spots on summer weekends...and what could limit those sites more, than a fin keel?

As I understand it, for reasons of national economic downturn in the nineties, other nations' cheap, fast, arguably appealing, mostly fin-keeled yachts virtually monopolised the new-boat-buyer's choice at that time and since, and thus they now also dominate the secondhand market, despite the high cost and limited choice of suitable berths, and the boats' own uselessness for enjoying so many of the appealing areas on their doorsteps...

...so, the problem isn't that bilge-keelers aren't wanted, but that almost everything we've been offered for several decades has been drawn with a very different, continental type of sailing in mind...and in the virtual absence of a UK small-boat industry, hardly anybody here buys an appropriate boat for the place they'll use it. The marketing men take care to push the performance benefits of a deep fin, they spatter the brochures with images from the Mediterranean scene which these hulls were designed to be at home in...

...and the future of UK coastal cruising under sail is intrinsically limited by the absence of any viable UK industry creating a home-grown, home-focused product. Blooming tragic.

By the by, what is wrong with Legend yachts? I don't admire their styling, but I approve of their designer's breadth of mind.

Dan
I think the "drying anchorage ( for cruising)" bit is really only a figment of many peoples minds. I see very few boats out cruising actually in such places. Perhaps they do 1-2 a year & that is it.

On permanent moorings, then yes, but when I let moorings to bilge keelers most owners are concerned that there is plenty of water under them at low tide.

My 31ft boat draws 1.800 which is possibly a bit more than most 31 ft boats
Except for running aground in Bradwell creek because I have arrived too soon ( a benefit of fin) I have never felt my fin keel a problem in 12 years of ownership & 23-25Kmiles. No way would I want bilge keels, because of the poor windward performance among other things ( such as the agro applying antifouling)

When i have anchored in shallower water - such as Walton Backwaters I do not take ground for long & the keel settles in the mud a fair bit anyway.

As for cutting corners in shallow water, there is not that much difference. An earlier post talks about going through the Swin Spitway. That can be a problem for me at low tide but I just time the trip a bit better & trips from reasonable distance away - ie Boulogne- do not muck up timing that much to get it right