Bilge v Fin

Lakesailor said:
I think I'll go off and top myself.

Yardsticks only measure the performance of existing boats (and their crews).
Existing bilge keels are generally a compromise for shallow draught, drying out purposes.

It is not a level playing field.
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Biggest variable is often the nut on the end of the tiller.
Keel type can be less important than a clean hull, folding prop etc.
I've sailed Hunter Duettes quite a bit years ago, they go well enough, but I wouldn't race one seriously. The recent Sadlers go very IMHO too.
Some of the older offerings are real dogs upwind IMHO though, I suspect that not only was the keel poorly designed, but the rig was never optimised around it.

But people still get places in them.
 
reeac said:
Let's have some numbers: Portsmouth Yardsticks -

Sadler 25 TK 1117, FK 1060....5% difference
Sadler 32 TK 1045, FK 1025 ... 2% difference

etc., etc.
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If the difference in performance is that small, it hardly justifies Ben Meakins' statement that 'Twin and bilge-keeled boats are designed to dry out - it's why their designers put up with the reduced performance that such a design entails'.
 
When comparing such aspects of a boat design, I think it's important to talk with a designer who actually sails his own creations ...

So - have a chat with Brent Swain - his fin and twin keel designs are identical except for the keels, and his experience is that the twin keel has an equal or better performance, as well as being more convenient for taking the ground. Hence very few of his fin keel designs have been built.
 
jimbaerselman said:
For racing performance on a given hull, all other things being equal, single keel wins (illustrated by yardsticks). The biggest advantage of a single keel is when going to windward; the boat points better, and has less leeway. It's a basic fact of hydrodynamics - long and narrow creates much less induced drag for a given side force.
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In theory maybe but, windward performance on many modern boats isn't good, as illustrated when our twin keeler beat two Jeanneaus which came as a big surprise to me - and them I suspect. Downwind they would have left us standing. A boat with a high aspect keel, spade rudder and shallow forefoot can't get a grip on the water compared to a longer keel(s), skegged rudder and deeper hull section forward of the keel. As someone mentioned earlier, there are of course variations in twin keels - ours were quite splayed, not vertical.

So we come back to - which twin keel and which fin? As you say, there are many other benefits of twin keels and now having a fin keeler, I can't go to some of the places I used to dry out in.
 
ghostlymoron said:
If the difference in performance is that small, it hardly justifies Ben Meakins' statement that 'Twin and bilge-keeled boats are designed to dry out - it's why their designers put up with the reduced performance that such a design entails'.
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Even a 2% difference is huge in racing terms.
Don't forget that most of the disadvantage is upwind, so you are looking at a 4-10% disparity upwind.
There are a lot of bilge keeled boats out there that don't point at all well, but then again, there are also some fin keel cruisers that don't point.
I'm not sure IRC gives bilge keelers a fair crack of the whip either. IRC is a measurement based handicap working on the predicted hull resistance and sail carrying ability of a well designed boat of given dimensions. It does not give credit to badly designed boats. (except via age allowance).
I don't know if the figures quoted were IRC or some imitation such as the ISC yardstick.
Anyone got any good data of twin keel boats doing well in races?
 
Lakesailor said:
3 or 4 times?

Don't forget most bilge keels you see are stubby little legs that are attached to the bottom of a floating caravan.
Most bilge keelers were not designed to do other than draw less than a fin and allow the boat to sit down without falling over.

The comparisons being drawn are not starting from an equal footing.
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LakeSailor that really isn't fair ! Having owned two twin-keelers - a Macwester 26 (which conformed almost exactly to your description) and a Sadler 29 which most definitely didn't - there is an enormous difference. The Sadler would not go to windward quite as well as the FK version but it had relatively deep draught (4 ft as opposed to 2ft 9in for the Macwester) it really sailed rather nicely to windward - we regularly short-tacked up the Swale. The FK S29 has a draught of 5 feet but you do have to bear in mind that the outward-angled keel will reduce that difference. The only disadvantage was that in a short chop and decent wind the windward keel did slam a bit but only if she was pushed !

Our current fin keeler sails like a dream but I still miss the quiet creeks and drying out. Would definitely think again about the ability to dry out when we have to change the boat.
 
Bilge keels

Over many years I have always been pleasantly pleased with the performance of bilge keelers. Once the speed picks up over 3 knots upwind performance is fine although a fin keeler can often point higher. An unexpected benefit has been a comfort/safety issue. In really difficult breaking seas you will make more leeway but often get a more comfortable and drier sail. A key issue is to reef early. a bilge keeler will perform best not too heeled. Wishing all good and safe sailing.

Barry
 
pragmatist said:
LakeSailor that really isn't fair !
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Just like all those who point to PY who are mainly comparing race designed boats to family cruisers, because that's the way designers have been building boats.

I had a bilge keeled boat which was rubbish. A slug downwind, made leeway like a crab and slammed the windward keel before inevitably rounding up.

I had a fin keeler which was quick and agile.

But although they were the same length they were miles apart in design.

Certain points were better in the bilge-keeler I felt. On a beam reach in a steady breeze it was a match for similar length boats
 
barryalan said:
A key issue is to reef early. a bilge keeler will perform best not too heeled. Wishing all good and safe sailing.
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I couldn't agree more. When I sailed against the moody 36 I was under full sail and no furls in a force 5, upwind.:eek: We were sailing at 5 knots. We had passed a cardinal approx mile be hide us but had drifted half a mile to leeward. Our leeway was approx 30-45 degrees with 30 degrees of heel.

I put in two reefs and we now sailed along at 5.8 knots with almost no leeway.
 
Lakesailor said:
Just like all those who point to PY who are mainly comparing race designed boats to family cruisers, because that's the way designers have been building boats.
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I don't understand. I compared a FK with a TK Sadler 25 and same for a Sadler 32. Is one race designed and the other a family cruiser? Bringing in PY s gets away from all the clean/dirty bottom, skilled/unskilled crews/anecdotes re. beating an AWB to windward etc. and quantifies the FK/TK argument.
 
No. You don't understand.

I keep saying, but no-one seems to have taken it on-board. Have you read the link in my first post?
The boat needs designing as a bilge keeler from the start with all the foils aimed at providing performance in that configuration.

I say again.
Comparing existing boats, designed as fin keelers that have had bilge keels added as an option is not a fair comparison. It does not quantify the FK/TK argument, it shows that the boat is quicker in the configuration it was designed for.

That's like putting M&S tyres on a BMW and then saying the ride isn't as smooth and quiet as it was with OE tyres.
 
Lakesailor said:
No. You don't understand.

I keep saying, but no-one seems to have taken it on-board. Have you read the link in my first post?
The boat needs designing as a bilge keeler from the start with all the foils aimed at providing performance in that configuration.

I say again.
Comparing existing boats, designed as fin keelers that have had bilge keels added as an option is not a fair comparison. It does not quantify the FK/TK argument, it shows that the boat is quicker in the configuration it was designed for.

That's like putting M&S tyres on a BMW and then saying the ride isn't as smooth and quiet as it was with OE tyres.
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Don't think that's fair - many of the boats mentioned so far have been DESIGNED with twin keels, some with performance as a priority (Hunters by Thomas, RMs - and you could add Feltham designed boats) and some not (Macwesters, Colvics Snapdragons et al). In many cases fin keels were offered as options and in most cases sailed better, particularly to windward. In some cases this difference is very small, such as the difference you can get with shallow/deep keel options. Quite often the boats from the first category sail at least as well or better than boats of similar size and style.
 
I don't see how you see my comments as unfair.
You have said just what I am saying.

The boat needs designing as a bilge keeler from the start with all the foils aimed at providing performance in that configuration.
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Design a good boat for twin keels and they are good.
Design a boat as a caravan with stabilisers and that is what you get.
Compare boats designed as fin keelsers with the twin keel option and of course they won'y be as good.
 
Lakesailor said:
No. You don't understand.

I keep saying, but no-one seems to have taken it on-board. Have you read the link in my first post?
The boat needs designing as a bilge keeler from the start with all the foils aimed at providing performance in that configuration.

.
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I saw a boat a few years ago with actually three keels with ballast provided by the centre one and the other two added to provide resistence when heeled to windward.

God it must have sailed like a dog.

I can't remember its name but it was something like

Saab Open 70


I don't think they caught on...



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