Twin/bilge keels, what to expect?

gunnarsilins

gunnarsilins

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www.eilean.se
While looking for a shallow draught long distance cruiser able to take the ground the bilge/twin-keelers (same thing I assume?) came into my mind.
But beeing from Sweden I have absolutely no experince from this keel configuration!
I realize that a twin-keeler must be slower than its fin-keeled sister. But in %, how much would you suggest?
Also, are there any other drawbacks apart from the less spectacular performance?
Can they be sucked into soft mud and never come up again? /forums/images/graemlins/shocked.gif
Are there any horror stories of twin-keelers capsizing when dried out on un-even sea bottom?
 
It is interesting Gunnar that twin bilge keels have never really caught on anywhere but the UK isn't it? I think there are no "perfect" boats, and obviously very many satisfied bilge keel owners, but the drawbacks are several.
Apart from a reduction in windward performance, drying out on a flat hard sand bottom is fine, but with wave action you will get a fair amount of "bumping" in any exposed bay which stresses the hull, keel joint. Splayed out keels put an angled thrust on the joint too, and most wasterlies and others with this configuration suffer from leaks here and periodically have to re seal the joint. If ever surveying one of these look carefully for cracks around the joint too....
The other problem is if you hit soft mud one side and something hard the other you fall over! Not good.... Repeatedly drying out in mud forces splayed keels outwards too.... Not good either!
If you want to dry out, why not have either a lifting keel, or dare I say it a catamaran????? As a cat enthusiast I would say that wouldn't I? But if I sailed your waters I would think a cat ideal and with long, low aspect ratio fixed keels and a draught of less than a metre, able to take the ground anywhere, and able to sail on wet grass!! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif
 
There is a very interesting article about this very subject in the current issue of either Practical Boat Owner or Sailing Today ( can't remember which ).

When looking for a boat myself recently I automatically ignored bilge keelers but it seems that the more modern designs have resolved most of the performance problems.
 
They did not prevent Shane Acton circumnavigating in a marine ply 18' Mk1 Caprice. In our club, with moorings in a drying harbour, about 20 bilge keelers and one lift keel - no fin keels.
 
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Apart from a reduction in windward performance, drying out on a flat hard sand bottom is fine, but with wave action you will get a fair amount of "bumping" in any exposed bay which stresses the hull, keel joint. Splayed out keels put an angled thrust on the joint too, and most wasterlies and others with this configuration suffer from leaks here and periodically have to re seal the joint.
(Catamarans have)... a draught of less than a metre, able to take the ground anywhere, and able to sail on wet grass!! /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif

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As a Bilge keeler supporter can I counter this somewhat biased - and I might say jaundiced - view on the breed. Taking the last point first, few Bilge keelers exceed a metre draft, and I am not sure what level of 'dew' Boatmike gets in his part of the world but.....!

The reduction in windward performance is not necessarily so: Sadlers conducted a test back in the 80s between their standard Bilge and Fin keel versions: They found close hauled the fin was slightly faster but pointed no higher. On a reach there was no difference, and off the wind the Bilger was slightly faster!

That is not to say all BKs go well to windward! Some designers - I would say many - simply did not put big enough keels on! The result was generations of boats that pointed well enough, but sailed sideways close hauled! I suspect the lure of 'shoal draft' was the problem. My current Bilge Keeler (a 50s desgn MG Eventide 26) makes up to windward as well as any boat I have owned. But then MG knew how to design 'proper' shoal draft boats for East Coast use!

But I really do take issue over the remarks of splaying and grounding. A properlydesigned Bilge keeler will be engineered to take the ground safely in adverse conditions. In 40 years sailing Bilge Keelers I have yet to own a boat that has had these problems. I have seen three which have suffered - one a Westerly Centaur where the keel bolts had losened and splaying had damaged the mouldings - and this is a known probem with older Centaurs - caused I suspect by owners failing to check the tightness of the keel bolts every couple of years as recommended by Westerly - so arguably lack of requiree maintenance. The others were a MkIV Caprice one builder took a short cut, and puit less reinforcement in the rear end of the moulded keel - resulting in splitting and cracking where the keel is forced up through the hull, and third was a plywood boat with the keels forced up through it. ? rot as the cause?

ALL the other bilge keel failures I have seen have been the result of stranding or heavy grounding in situations in which a fin keeler would have fared equally badly or worse! ANY boat which gronds in rough water is likely to be damaged, and a fin keeler going over as the tide recedes will be putting far more strain on its keel and hull than any bilge keeler.

A bilge keeler MAY get away with stranding on rocks with its hull undamaged. A fin keeler is far more likely to suffer a hull breach in the same circumstances. I have seen both events (not my boats thank goodness!) and reckon on balance the BK configuration tends to have a bteer chance of survival as it stays upright.

As to 'falling over' - yes it can happen. But not every time like a fin keeler! But because the COG is so low across a relatvely wide base, the hull has to be tipped an incredibly long way before it goes over.

But who puts a boat aground deliberately without checking that it is safe to do so! - i.e. reasonably level, clear bottom to land on. In 40 years sailing from drying harbours I have never yet seen or heard of a BK falling over, except when the Glaslyn at Porthamadog changed its course overnight and cut through the moorings at Borth in the late 60s - I believe every boat involved was toppled over and sunk as the river dug a new bed for itself.

Balance that with the convenience of shoal draft, the ability to take drying (therefore cheaper!) moorings, and the ability to beach for maintenance, picnics etc, I personally wonder why the non racing fraternity bothers with the hassles of fin keelers? Many many BKs have excellent racing records too at Club level!
 
Probably an ideal place for them then. As far as Shane Acton is concerned I think it is like saying people have gone over Niagra Falls in a barrel. Very brave, probably quite mad, and I certainly wouldn't!
 
Well "Oldharry" all I can say is that having sailed, built, repaired and otherwise mucked about in boats for fun and for a living for over 50 years I am not either biased or jaundiced. I have owned and sailed gaffers, ketches, modern sloops, and cats in wood, steel and GRP from 20 to 70 ft and can tell you one thing for certain old chap. There is no perfect boat! All boats are a compromise. Bilge keelers have their place. But to suggest that any bilge keeler can have the performance of a good fin keeler is nonsense. Some, as suggested by the recent press article, and by yourself, do very well against other boats of similar size with shoal draft fin keels, but neither bilge keelers or cats can compete with a good deep fin keelboat to windward.
My remarks regarding taking the ground are based on many experiences which are well documented and known by any boatbuilder. As you say yourself, even westerly suggested that part of regular maintenance should be to check keelbolts regularly. Why? Because flexing of the keels causes them to loosen thats why! If the boats never take the ground or do so with care it's fine, but the idea that they can take the ground anywhere with impunity is rubbish. If it is hard flat bottom in a sheltered harbour they do very well. Where there is soft mud of any depth and a bilge keeler settles in to it so will a fin keeler, and many do. Cats are even better at it.
On another thread I started on cat performance I just told another poster that he is protesting too much defending cats against everything else when not being attacked by others. Cats are not perfect, they have drawbacks. To suggest otherwise shows lack of experience of anything else. Similarly bilge keelers are far from perfect but suit some purposes very well. To suggest nothing has faults is biased, jaundiced, and just plain silly. You are of course like everyone else on this forum entitled to your opinion and can call me jaundiced and biased if you like, but forgive me then for suggesting that you are more biased than I.
 
A modern well designed Twin keel boat will sail to windward almost as well as an identrical fin.Off the wind probably no real difference.

If you sail in an area where harbours dry out at Low water then twin keel boats are much easier as you dont need to rig legs or lean against a wall.

I have never heard of a twinkeeler not refloating due to being stuck in the mud.

One disadvantage of twin keels is that if you do ground on the ebb tide usually you are stuck as you cant reduce the draught by heeling as you can with a single keel.Also if drying out on a muddy river bank a twin keel boat will usually lean away from the bank where a fin keel will dry out upright Or can be encouraged to lean towards the bank.

If you intend drying out in harbours that have hard sand bottom then twin keels are ideal for stress free cruising.If you dont intend drying out much then you may as well go for the slightly better performance of a fin.

Personally for cruising in shallow estuaries I think a lifting keel is the answer.
 
I posted a link a while ago from an Canadian naval architect's site in which he argued the case for twin (bilge) keels. Bray Yacht Design
I had a bilge keeler at the time. Not a cutting-edge design. Some points he made were born out by my experience.
-On a broad reach a bilge keeler can be very quick.
-Running they can be extremely sluggish.
-Close hauled they lose out by making a lot of leeway.
-Heeling can be reduced by the leverage of the windward keel and the leeward keel can be more vertical, depending on the splay in the design.
-In extremis their behaviour can be unpredictable as the geometry of the forces moves about below the waterline as they heel.
-Rudders generally stall more easily as they are out of the flow (unless twin rudders are employed)

On balance, as I sail in non-tidal and quite deep waters I find a fin keel much better, especially with a mind to the leeway. Simple fact is I can get up the lake against the wind in half the time.
On fiercely tidal estauries a bilge-keeler can be less useful than a lifting keel yacht. If you touch on a falling tide the lifting-keeler can lose a bit of draught and escape whereas a bilge-keeler may be stuck.

Horses for courses.
 
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. Simple fact is I can get up the lake against the wind in half the time.


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Simple fact is that it is nonsence ,to suggest that a fin keel version of a boat will be twice as fast to windward is totally off the wall.more like 5 to 10 % in my experience.
 
One thing that has put me off (and this related specifically to Sadlers) is that the windward keel can pound / cause noise when well heeled in waves. I don't know if anyone can confirm this, or it's just another old wives tale? I have to say that with all the drying harbours around my part of the world, I'm favouring the idea of a bilge keeler next time.
 
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the windward keel can pound / cause noise when well heeled in waves.

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I get a banging/slapping sound at times if too well heeled. Didn't half give me a shock when I first heard it, as I was used to fin keeled boats. However the excess heeling is usually because I haven't reefed early enough (Virgo Voyagers are best reefed early and sailed as upright as possible).

However, just to confuse the thread somewhat, my boat is a triple keeler with a short ballasted centre keel and two bilge keels that finish a few inches shorter than the centre keel. This has the advantage of being able to persuade the boat to tip slightly which ever way I prefer it to when drying out.
 
Hi Gunnar

Don't let Boatmike put you off with all his nonsense! He seems to have hijacked your post to defend catamarans, presumably out of some inferiority complex about his own boats windward ability. Unfortunately you all too often get people posting on here who use an innocent question as a way of forcing their boat choice on you!

So let's stick to answering your post, here are some thoughts:-

1) I can only echo what Old Harry and others have said. I've sailed Twin / Bilge and Fin keel boats for 30 years and have never seen or heard of any bilge / twin keel boat ever falling over when dried out. Occasionally they may dig in at odd angles or slightly stern / bow down but despite looking alarming, it's nothing to worry about!

2) They can be uncomfortable when first touching the ground (just as any boat would be) - they tend to bounce a bit from one keel to the other if there is any kind of sea - but any that have been built post the early 80's will have been well made and engineered properly. Like Old Harry said, some early Westerly's did have problems but these were pioneering times and most will have been corrected now. The stresses and forces that have been highlighted weren't always understood when they first started making them out of GRP back in the late 70's.

3) A well sailed twin keel boat will perform at least as well as an average sailed fin keel boat. I have added a feathering prop and some fancy sails and my twin keel Hunter 31 is faster than every Bavaria 36 that I have been alongside this year. Whenever someone tells you they don't go upwind ask them if they have actually sailed on a twin keel boat? Most haven't or have sailed very early designs. Like others have said, early designs had slab sided keels, with little or no tow- in or splay - these boats won't sail well and I dare sare their fin keel variants didn't sail well either. Yo get good and bad boats of any type! Ocasionaly the windward keel can slam a bit but this is generally a sign that it's time to reef and a quick reef soon stops the noise (not that it is anything to worry about anyway and you soon get used to it)

4) Stability is equivalent to a fin keel. Numerous stability curves for various boats such as the S290, British Hunters, Hunter Legends etc have shown that. Put it this way a fin keel boat with in mast furling would probably have a worse stability curve than a the same boat with twin keels and no furling. I also believe that twin keels play a significant role in damping the motion when at sea - especially downwind where they roll a lot less.

One thing that never gets said about twin keels, which I think is a fair criticism, is that personally I don't think they motor as quickly or are as quick off the wind IMHO. The other specific advice to you is that I see your current boat is quite big. I would be wary of buying a twin keel boat bigger than say 35' only becuase it may be difficult to re-sell given that most people choose fin keels above this size.

So in summary - what to expect?

Expect a lot of cruising fun, with near equal performance to a fin (or improved performance if you can be bothered to tweak a few things) and stress free tidal calculations....oh and the ability to get to a lot of places that other boats just won't get to!
 
You're selectively choosing the only bit of my post that is a positive for my current boat.
The link I give supports the concept of bilge keels and my own points are similar.

The reason my current fin keel boat manages so well against my old bilge keel boat is that they are different types of boat. The current one is the same length but 2/3 rds the weight and a lot more slippery.

The leeway my old boat made was the key to awfull windward performance. When beating up the lake against a Northwesterly you are putting in a lot of tacks and each one magnifies the lost ground of the preceding ones.

wind.jpg
 
I think Matt makes a good point. The difference in performance (if there is one) is lost in other factors. A folding prop, good sails, clean hull and a competent helmsman make more difference than the number of keels.

One potential disadvantage is that if you do run aground, heeling the boat over to reduce the draft doesn't work! That said, you do get the benefit of worrying less about running aground, cos in extremis you can just wait for the next tide.

One minor benefit not mentioned, is antifouling is a doddle. No props to move around to paint behind!

For me, having owned both types, the shallow draft and ability to dry out for fun or maintenance are the two biggest plus points of a twin keel. I can honestly say I don't feel any inferiority in the performance stakes.

Simon
 
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A well sailed twin keel boat will perform at least as well as an average sailed fin keel boat.

<span style="color:blue">But why would a good sailor, sailing well on a bilge-keeler become an average sailor, sailing averagely on a fin-keeler, surely the discussion is assuming the same skipper but different boats. </span>

One thing that never gets said about twin keels, which I think is a fair criticism, is that personally I don't think they motor as quickly or are as quick off the wind
<span style="color:blue">
I think I made that point above </span>

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You did indeed make the point and I guess I was just echoing it. Frankly I'm just challenging the stereotypical view handed down at successive sailing club bar discussions that "bilge keelers don't go to windward" and trying to give an honest appraisal of where there are strengths / drawbacks. How many people decided against buying a twin keeler because they were warned off about the windward ability I wonder? However I think my point about average vs well sailed applies. There are days when I am very average...you know, can't be bothered to shake out that reef etc and days when I try really hard and tweak every last rope. And then there are days when I'm really trying /forums/images/graemlins/cool.gif
 
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