Bilge keels are Better??

World of difference between "Bilge Keels" and "Twin Keels"

Many boats with two keels are poor performers because of inefficient shape, positioning and shallow draft. Many 70's 80's boats were like this because of the demand for shallow draft, ability to dry out and the simplicity of moulding vertical keels in the hull.

However, later developments where draft was increased and more "science" was applied, performance improved dramatically. Sadlers, Sea Wolfs and Hunters were examples of good performing two keeled boats. However, they fell out of fashion as boat size increased and marinas became the natural home of new boats.

There are still some examples - the French RM range is one where two keels are used on hiigh performance boats.

The reference you give is in the same line of argument as some designers such as David Thomas use to explain why they can get good performance out of boats with two keels.
 
Strikes me that they are not comparing like with like in their assessment. Bilge keels are great for their squatting purpose, but not as good as a single fin keel for sailing qualities - otherwise all those racing yachts would be using bilge keels.
 
The diagram looks like they are comparing a twin keel boat with a single keel boat of the same draught. Usually the twin keel option has a shallower draught than the fin and it is the increased draught that gives the increase in performance. I must declare an interest but I believe that the more modern splayed twin keels perform much better than the earlier designs with moulded vertical keels. The downside is that the windward keel root breaks the surface and slams when hard pressed in a chop.
 
The modern Open 60s and the like have split the ballast and lateral resistance jobs of the keel by putting the ballast in the canting keel and the lateral resistance in TWIN dagger boards. So maybe there is something in it.
 
Bilge keels gained a reputation for poor performance as a result of some really slow designs from the 60s and 70s.Mostly with very shallow draft and vertical keels

In order to mould the boats the keels had to be vertical or they would jam in the mould when trying to seperate the two..

This was overcome (at a cost) by making split moulds that could be bolted together down the centreline then removed from the new boat hull by seperating again and removing in two pieces.

A modern design bilge keeler with splayed out hydrodynamically designed keels will perform very well.

Unfortunately now that most boats live in marinas the market for bilge keels isnt strong so you dont see many new designs on offer.
 
'now that most boats live in marinas' is this really true? I see a lot of boats on swinging moorings everywhere I go. I suspect that most forumites are not the types to pay marina fees.
 
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Strikes me that they are not comparing like with like in their assessment. Bilge keels are great for their squatting purpose, but not as good as a single fin keel for sailing qualities - otherwise all those racing yachts would be using bilge keels.

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No - you're not comparing like with like. There have been a number of trials comparing bilge keels and fin keels on the same hull and the differences in performance have always been very small. OK these were all on cruising boats like the Sadler 34 where the fin was not very deep and rather long. Nevertheless I suspect the difference would also be small if you compared on a cruiser racer hull with bilge keels almost as deep as the fin version.

Problem is of course that you cant really have bilge keels 2.5 metre deep like the racers have fins, can you? You only chose bilge keels if you want shallow draft / drying out and by definition this means they are shallow keels. So whats really happening here is that you are choosing shallow keels and these dont perform as well as deep fins.
 
Probably not true, however, the issue is more about what buyers of new boats want as it is those who are more likely to inhabit marinas. There are huge numbers of twin keel drying out type boats giving good service, just limited demand for new boats. Only ones on the market now are the Sadler 290 (maybe) the RMs and Legends - although the last named has made little impression despite being built with twin keels specifically for the perceived UK market.
 
I have had 2 Hunters(British) with twin fins & they both sailed OK.However having raced bigger fin keelers when I sailed my current boat(a fin keeled Moody 31) I realised that there is a difference.The fin keeler points better without a doubt & doesn't slam to windward.Last summer we were beating up the Blackwater & a friend in his W.Storm could not catch us in his twin keeler.He was having to sail a few degrees more off the wind.When we got ashore he reckoned it was 4/5 degrees.I didn't think it was that much.It may be that a twin keeler with the same depth would sail as well as a fin but I don't know of any that you could compare.If you look at the handicaps on www.byronsoftware.org.uk/bycn/byboat.htm the handicaps of the same boats twin against fin are always slower.Some by alot,some not so much.The advantages of twin keels are obvious but when it comes to speed fins are quicker.Whether that makes them better is another matter.
 
As I keep saying "There is no such thing as a perfect boat" If there was we would all have one and they would all be the same. This is like the "catamarans are rubbish" brigade. There have been good bilge keelers and crappy ones, just like catamarans, fin keelers and even long keelers. Generalisations are a waste of time. What do you want it for? Does it perform these purposes well? Yes? OK then it's a good boat! But the same boat will be rubbish to someone else who probably wants the boat for something entirely different.
 
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What do you want it for? Does it perform these purposes well? Yes? OK then it's a good boat! But the same boat will be rubbish to someone else who probably wants the boat for something entirely different.

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Probably the sagest advice ever written on these forums!
 
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As I keep saying "There is no such thing as a perfect boat" If there was we would all have one and they would all be the same. This is like the "catamarans are rubbish" brigade. There have been good bilge keelers and crappy ones, just like catamarans, fin keelers and even long keelers. Generalisations are a waste of time. What do you want it for? Does it perform these purposes well? Yes? OK then it's a good boat! But the same boat will be rubbish to someone else who probably wants the boat for something entirely different.

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Spot on Mike.

My best description of any boat is that it is a collection of compromises.

Avagoodweekend......
 
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What do you want it for? Does it perform these purposes well? Yes? OK then it's a good boat! But the same boat will be rubbish to someone else who probably wants the boat for something entirely different.

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Probably the sagest advice ever written on these forums!

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Quick, report him and get it deleted! /forums/images/graemlins/wink.gif
 
The keel wetted area is the key to drag, and this is clearly greater (equal weight assumed) with twin keels than a fin.

But the greater depth of a fin will exercise more hydrodynamic influence, enabling higher pointing over twin keels, and better performance.

The subject is open to many interpretations, as you realise, but those of us who have sailed twin keels, endured the bashing to windward (sort of) etc, will tell you fins, by and large, deliver better sailing.

In the years I sailed twin keels, I never did really benefit from the presumption of easier shallow water sailing. It was and is a myth. If you have a drying mooring....

Finally, when you look round the world, it has to say something that UK almost alone still sails twin keels - a declining share of the fleet.

PWG
 
it is very difficult to drill an 80mm bole through a fin keel fit an axle and still maintain balance whilst clearing the surf line readey for a final tack up the beach to the icecream kiosk. Us bilge keelers on the other hand have the perfect platform to hang the axle and tractor wheels off to facillitate a perfect exit on the most shelving of beaches... oh s**te that was all out loud wasnt it? /forums/images/graemlins/smirk.gif
 
Re: Wot\'s \'better\'??

"My best description of any boat is that it is a collection of compromises."


As this debate appears more erudite than many we've seen on this issue I'll venture to qualify oldsalt's statement above:

A good boat is a good boat - it just IS. But few of us ever get to meet the designer so often don't know the thinking behind the the product (you should hear David Felpham on the subject of twin keels!).

We have progressed from technological limitations which dictated how twin keels could be angled but if the brief was maximum accommodation in a hull that would take the ground and that is achieved then well done say I.

And you expect it to sail too? OK - but how well? Just so-so or better than that?
Clearly the deeper the keel more close-winded the boat. It is heartbreaking (and sometimes dangerous) to leave Cherbourg close-hauled for the Nab and find yourself downwind of the Owers.
By contrast, popping into Hillhead (where?) for lunch does make you feel smug!
But is that a better feeling than coming out of Pompey under spinnaker and overtaking yachts under engine?

Sorry, but the 'compromise ' is your own particular cross, nothing to do with the boat, albeit coloured by the ongoing love affair.

One year we brought the Sigma 33 back from the Morbihan and visited every port you could enter with 6ft draft. Some years later on a twin keel Seawolf 30 we ticked off all the watering holes in the Baie de St Brieuc, places we simply couldn't access before.

Which was better? Can't say. And shouldn't compare.
One thing is sure - I hate compromise. But will cast a vote anyway . . .

Of hundreds of boats that sail past my window I must respect a local Prout Snowgoose (that's a 37ft catamaran). Admittedly I've never seen him go out in gale but always seems to point quite high and sails the socks off anything else around. I'm familiar with multihulls but this one does have an edge.

Food for thought maybe?
 
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I never did really benefit from the presumption of easier shallow water sailing. It was and is a myth.

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Some myth! We rarely dry out completely but the benefits of being able to touch the bottom for a couple of hours at low water can't be overstated in the crowded anchorages of the South Coast.
 
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