Disadvantages of a shoal draft

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Oscarpop

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As I recall the shoal draft boat makes compromises in the pointing ability of the boat by a couple of degrees. You also have to reduce your sail area a little sooner.

Anything else?


Many thanks.
 
A shoal draft keel model compared to the full length keel model is likely to have more weight at the end of the keel to compensate for the reduced length.

The difference in pointing for a modern design is likely to be small. So if you take this small effect and multiply it by the fraction of time spent beating (about 30% is a figure could be used), the net loss in performance is negligible. for cruisers.

This is true for even some older designs such as Rival yachts i.e. the designers knew what they were doing. As has been pointed out on another thread, two yachts from the same stable and model, but one with a fin and one with bilge keels, were in a race, the bilge keeler was sailing better up wind.
 
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shoal draft and taking the ground

I think that it is the ability to take the ground that is more impoortant than the depth of the keel

you can do one heck of a lot of sailing around the UK in thin water

but only if you are not frightened of going aground

I had a fin keel sonata and a drop keel eboat

in my humble opinion the eboat outsailed the sonata on every point of sail apart from a beat into an east coast chop

http://www.keepturningleft.co.uk/ktl-scuttlebutt/scuttlebutt-47-east-coast-chop/


and I think that was down to the hull shape

the slug does okay in it though

the reason the slug works for me is that it is a go anywhere boat

not many deep keelers up here

http://www.keepturningleft.co.uk/category/the-nene-wonderful/


so.....

my advice.... the assumption behind the initial question is slightly wrong

of course if its crossing oceans you need to do.....

then everything changes

Dylan
 
Shoal draft

I have an Oceanis 321 that is described as shoal draft at 1.3m with a bulbed fin. The shoal draft has to be considered together with the hull shape as the two combined are a compromise. To me as a relatively inexperienced sailor it means that I don't have to worry as much about running aground and gives me more confidence to go places i otherwise wouldn't. A big plus in my own particular circumstances. As for going to windward, I think my boat goes very well but if it doesn't I switch on the engine. If you are the kind of sailor that likes to push the limits I dare say a deep or long keel is more suitable. For me the most important thing is that my wife sails with me. For that to happen my boat must sail relatively upright, go where she wants to go and have comfortable accommodation. The only downside I've found is that if the sea picks up, she slams, big time.
 
The questions implies a comparison between standard and shoal draft versions of the same boat and in that case the difference in pointing ability need not be very marked. The designer will have compensated to some extent for the shallow keel by putting more ballast lower down, perhaps.

A more difficult comparison is between, say, a bilge keel boat and a deep fin keel boat. Many other factors will come into play - hull shape, entry, sheeting angles and so on.

With lifting keel boats there is likely to be less difference because with board down the boat is back to being deep draft.

And, as Dylan, says the question of 'will she take the ground upright' introduces further design compromises.
 
It is really to compare boats which are the same but with different keels.

Can someone please explain the problems of a shoal keel in an ocean crossing. Is is as I expect because it reduced stability
 
Never seen any direct comparison under controlled conditions with modern fin keeled boats, but you would expect a loss in upwind performance and greater leeway.

As you know, I have a shoal draft Bavaria - chosen deliberately to have access to the canals. The basic design is not performance orientated anyway, and I have in mast furling which is supposed to be less effective. I have never sailed a deep draft version, although I have sailed another shoal draft one, and if I closed my eyes would not be able to tell the difference between the two boats, so I think mine is as good as it could be of its type - and probably better now I have new and better sails.

Overall the boat meets my requirements. I try not to beat to windward in higher winds, and this is definitely its weakest point, but how much of that is due to the keel and how much the hull shape and high windage I don't know. Otherwise it is an easy going boat with good directional stability and once off the wind seems as fast as other similar sized boats. Now I have it in Poole the shallow draft is an advantage as it means that more of the harbour is open to me. As I often sail single handed or with only one less than keen crew, easy handling is high on my list of priorities, and much higher than ultimate performance.

Having said all that, if I was only sailing in the Med or offshore, I would choose a deeper draft, although not sure about the latest skinny keels with T shaped bulbs on the end. Seems to me that they are good when you are really going, but might stall at lower speeds and lead to poorer directional stability.

Overall, I think you have to consider your priorities first and then choose the boat afterwards. In the case of draft I think the overall differences are marginal, and if going through the canals is high on your list of priorities then choose a boat that will do it. The loss if any in other types of sailing are likely to be small. In particular in the Med, the priorities are good light weather performance (if you want to sail as much as possible), good engine as if you want to undertake longish passages you will do a lot of motoring, comfortable well ventilated living space down below and open outdoor living space as you will spend a lot of time outside. Just about sums up many of the AWBs - which is why they are so popular!

To answer your last question, don't think it makes any significant difference in ocean crossing. The stability is generally the same and in trade wind sailing you are off the wind most of the time. Different if you are planning to sail high latitudes in heavy weather when you would likely be looking for a different kind of boat altogether. One of the most successful ocean cruising boats (in terms of the number that have circumnavigated) is the Golden Hind, which is shoal draft at 1.2m - and a bilge keel!
 
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Oscarpop said:
As I recall the shoal draft boat makes compromises in the pointing ability of the boat by a couple of degrees. You also have to reduce your sail area a little sooner.
Click to expand...

I have experience with both and it is impossible to generalize because different manufacturers have different keel weights and shapes.

My experience with a Dufour 36 Classic shoal keel (with large bulb) was positive with good pointing ability up to 30deg off the wind at the expense of speed. I considered also that boat very stiff, being able to carry full sail close hauled up to 20kts apparent. However, even though I was able to point high, with the shoal keel I did not realize that I was drifting more.

Now with a deep fin keel and no bulb I point just a little more, I can sail a little faster, but most importantly I drift a lot less. This may mean sailing with wind directions that otherwise would have required motoring to get back home on time. However sometimes I whish I had the shoal keel, because there are routes that I can no longer take.

It is difficult to find the right conditions to compare two boats, who can find two twin boats, rigged exactly the same with just the keel as a difference?

However I would like to add this as an "aneddoct": The previous owner of my current deep lead keel boat had a friend who had a twin boat in the same marina, only with the standard iron+bulb keel instead of the deep lead version, and he said that when sailing on a long passage "he used to leave him behind".
 
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As already mentioned, a shoal keel will usually result in a little more leeway.

It will also have less 'grip' on the water in another way; after a couple of days of strong winds, the whole surface of the sea is set drifting that way, for some days later.

This surface drift layer is generally thought to be around 1 metre deep, so a keel getting to the still( er ) water beneath will be an advantage when going to windward.

However, especially with larger boats, the huge penalty of not being able to visit quite a few useful ports and canals, combined with the facts that serious punching to windward is rare - and there's always the motor, hopefully - would seem to make a good shoal keel rather attractive.
 
In the main: Less draft = more drift sideways; hence less efficient upwind. Shoal draft; able to sail on shallow waters. Bilge keels = more drag and therefore slower but ability to dry upright and cheaper moorings.

My boat is bilge keel therefore a bit slower and drifting more but I can go where others can not and "park" a much lower cost.
 
The keel does 2 jobs:-

1./ It produces righting moment. A shoal draft will produce less righting moment even if it's the same weight, so even with a bulb it will not usualy stand up to quite as much breeze.

2./ It acts as an underwater sail and produces lift. Most shoal keels are longer (front-to-back) in order to replace some of the area lost in depth and also o make them take the ground better.

In my view and experience (I've had both), unless you're going racing the shoal draft versions are much more useful and the difference in performance is negligable.
 
Shoal draft

It has been suggested by those who know that when abeam a breaking sea that shoal draft can be far better in resisting capsize. This because in a breaking sea the surface accelerates while the deeper water remains stationary hence a tripping action of the hull over the keel tip. Is this a real concern? I don't know and hope never to find out.
For me it is all about windward performance so a deep fin keel is best. However I did have a friend who had a keel closer to 3 metres on a high performance 30fter. She just had so much trouble finding deep enough water in our estuary that she migrated to the ocean. That depth did seem a bit over the top but it sure skipped along. Certainly different priorities in UK.
Many years ago I had a friend who built a 30ft plywood bilge keel yacht. I always wondered why bilge keel. It is the only one I have ever seen apart from photos of BK in UK.
good luck olewill
 
William_H said:
It has been suggested by those who know that when abeam a breaking sea that shoal draft can be far better in resisting capsize. This because in a breaking sea the surface accelerates while the deeper water remains stationary hence a tripping action of the hull over the keel tip. Is this a real concern? I don't know and hope never to find out.
For me it is all about windward performance so a deep fin keel is best. However I did have a friend who had a keel closer to 3 metres on a high performance 30fter. She just had so much trouble finding deep enough water in our estuary that she migrated to the ocean. That depth did seem a bit over the top but it sure skipped along. Certainly different priorities in UK.
Many years ago I had a friend who built a 30ft plywood bilge keel yacht. I always wondered why bilge keel. It is the only one I have ever seen apart from photos of BK in UK.
good luck olewill
Click to expand...

Yes, this is how the sailing ships - including Tea Clippers - operated, if a huge side load came on they would hopefully skim sideways.

In The Bible ( otherwise known as 'Heavy weather Sailing' by Adlard Coles ) he mentions a large lift keel yacht ( IIRC Curlew at 72' ) actually raising the keel in a survival storm for the same reason. Of course at that size a lift keel is just for grip on the water to windward, the ballast stays on the hull stub.

On the other hand, I have a 22' lift keel boat with 950 lbs ballast, 4'6" down when lowered so very stiff. One of the same designs which raced across the Atlantic did it with the keel up most of the time, in trade winds, and I know she's self righting with the keel up, but I suspect it may take bigger cojones than mine to actually raise the keel in a storm !
 
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