Hi, How can I increase pointing or decrease drift besides centering the sails. I heard that an "otter tail" shaped plate bolted to the bottom of a shallow keel would help. Before trying, anyone with some experience? Thanks, Bert
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AAAAAAH?
If I'm reading you right you are talking about attaching a large piece of material to the bottom of your shoal draft keel??? Well that would improve the draft and that generally has a good effect on pointing and drift but I've never heard of it being done that way. There would no doubt be less of a gain than just bolting on a full keel. And after all the fabrication costs probably just as expensive.
If I'm reading you right you are talking about attaching a large piece of material to the bottom of your shoal draft keel??? Well that would improve the draft and that generally has a good effect on pointing and drift but I've never heard of it being done that way. There would no doubt be less of a gain than just bolting on a full keel. And after all the fabrication costs probably just as expensive.
Prieus, Can you define the parameters a bit more?
What kind of boat are you sailing? Brand, size, year....? The more info you give us, the better we can answer your question. Being long winded is not a problem here.
Thanks for posting, r.w.landau
What kind of boat are you sailing? Brand, size, year....? The more info you give us, the better we can answer your question. Being long winded is not a problem here.
Thanks for posting, r.w.landau
Methinks he wants to convert a shoal draft ......
keel to Sheel type keel. The equivalent would be adding a 'beaver-tail' to the bottom of the existing keel, etc. http://marsmetal.com/newpages/keelhome17.html ... for further info of 'bolt-on' appendages to do what you want. (warning - I didn't say it would be cheap). After Hurricaine Floyd lessened the depth of many creeks on the northern Chesapeake, many boaters who keep their boats in their own backyards, etc. had their keels cut down and added exactly what you are probably wanting.
keel to Sheel type keel. The equivalent would be adding a 'beaver-tail' to the bottom of the existing keel, etc. http://marsmetal.com/newpages/keelhome17.html ... for further info of 'bolt-on' appendages to do what you want. (warning - I didn't say it would be cheap). After Hurricaine Floyd lessened the depth of many creeks on the northern Chesapeake, many boaters who keep their boats in their own backyards, etc. had their keels cut down and added exactly what you are probably wanting.
I ment "Beaver" tail
Sorry for the confusion. No pictures or drawings either. It was just hear say.
Sorry for the confusion. No pictures or drawings either. It was just hear say.
Boat Specifications
This is an O'day 39 1985. Actually the O'day 39 is a Jeanneau Sun Fizz build under license in the US. LOA 39' LWL 33.7" Beam 13' Draft 4'8" Displ 18,000lbs ballast 7,200lbs lead Displacement to lenght ratio 213.74 Sail area to displacement ratio 15.86
This is an O'day 39 1985. Actually the O'day 39 is a Jeanneau Sun Fizz build under license in the US. LOA 39' LWL 33.7" Beam 13' Draft 4'8" Displ 18,000lbs ballast 7,200lbs lead Displacement to lenght ratio 213.74 Sail area to displacement ratio 15.86
No Expensive solutions.
What I understand is that it looks like a beaver tail. Made from a flat 1/2 inch steel plate bolted to the keel.
What I understand is that it looks like a beaver tail. Made from a flat 1/2 inch steel plate bolted to the keel.
Please back-up a minute .....
Boat 'drifts' off to the side .................... . Have you corrected ALL the 'other' things that can reduce a boat 'skidding off to leeward'? Not letting the boat heel too far. Correct rigging tensions, primarily so that the jib/genoa doesnt develop a radical sag to leeward on the forestay. Mainsail correctly raised so that the boltrope on the luff is correctly 'stretched' to remove the 'preload' that the sailmaker designed in the sail (Very few cruisers ever do this). How OLD is the mainsail? and what is its 'general' shape? (A mainsail that is well used and is over several years of hard use will naturaly develop 'wierd' shapes .... that can easily be remedied.) What size (%) jib/genoa are you using and whats the approx. windstrength? On a furler or hank-on (piston hanks)????? How much weather helm do you have when the boat is in 15kts when on a beat???? What happens when you entirely let go of the tiller/wheel when on a beat? What angle do you see the wake coming off the stern of the boat when beating in to the wind? ... is it noticeable.? or is the wake coming almost 'straight' from the stern of the boat? .... are there a LOT of visible BUBBLES coming off the stern caused by the rudder? Does the boat 'suddenly' lose rudder control when well over on a heel when beating? A LOT of things will cause a boat to adversely 'drift' or skid off to leeward .... explain a little more and perhaps we can collectively help you work this out. Usually adverse side-slip or 'drift' or skidding off to leeward is usually a case of insufficient backstay/forestay tension .... etc. etc. etc. etc. etc. Hope this helps. ;-)
Boat 'drifts' off to the side .................... . Have you corrected ALL the 'other' things that can reduce a boat 'skidding off to leeward'? Not letting the boat heel too far. Correct rigging tensions, primarily so that the jib/genoa doesnt develop a radical sag to leeward on the forestay. Mainsail correctly raised so that the boltrope on the luff is correctly 'stretched' to remove the 'preload' that the sailmaker designed in the sail (Very few cruisers ever do this). How OLD is the mainsail? and what is its 'general' shape? (A mainsail that is well used and is over several years of hard use will naturaly develop 'wierd' shapes .... that can easily be remedied.) What size (%) jib/genoa are you using and whats the approx. windstrength? On a furler or hank-on (piston hanks)????? How much weather helm do you have when the boat is in 15kts when on a beat???? What happens when you entirely let go of the tiller/wheel when on a beat? What angle do you see the wake coming off the stern of the boat when beating in to the wind? ... is it noticeable.? or is the wake coming almost 'straight' from the stern of the boat? .... are there a LOT of visible BUBBLES coming off the stern caused by the rudder? Does the boat 'suddenly' lose rudder control when well over on a heel when beating? A LOT of things will cause a boat to adversely 'drift' or skid off to leeward .... explain a little more and perhaps we can collectively help you work this out. Usually adverse side-slip or 'drift' or skidding off to leeward is usually a case of insufficient backstay/forestay tension .... etc. etc. etc. etc. etc. Hope this helps. ;-)
Did some experimenting with my first wing ...
found that wings are very very delicate in regard to lift. On the Oday 272 the best pointing was with a 15-20 degree heel angle ... In light wind for example you can see a noticeable increase in pointing ability if you move crew leaward to force the 20 degree heel ... Under 20 degrees the wing flies at the wrong angle for good pointing ... over 20 degrees you simply side slip. You definitely don't want to try to sail low heel angles up like full keels like. Vic "Seven"
found that wings are very very delicate in regard to lift. On the Oday 272 the best pointing was with a 15-20 degree heel angle ... In light wind for example you can see a noticeable increase in pointing ability if you move crew leaward to force the 20 degree heel ... Under 20 degrees the wing flies at the wrong angle for good pointing ... over 20 degrees you simply side slip. You definitely don't want to try to sail low heel angles up like full keels like. Vic "Seven"
Out of balance here...
Rich, Thanks for your reply. However, the question is, how to improve the pointing ability of a shallow keel. All what you are refering too is correct and very importent but this is all above the waterline. We just need to find out if any changes under the waterline would help.
Rich, Thanks for your reply. However, the question is, how to improve the pointing ability of a shallow keel. All what you are refering too is correct and very importent but this is all above the waterline. We just need to find out if any changes under the waterline would help.
Thats easy .....
be sure that the leading and trailing edge shapes of the keel and rudder are close to the NACA "010" shapes/profiles. The 010 profile is 'generic' keel shape probably used by most of todays 'good' boat designers. This shape will give you close to the best shape and efficiency. The NACA 010 (dont have the other prefixes and suffix numbers of the '010' ... went somthing like NACA64010xxxx? but is simply called the famous/reknown "010") is a foil shape used in aircraft AND boat keels/rudders. Just do a websearch for "NACA 010"+"KEEL" NACA was the predecessor of NASA. I've reshaped most of my (racing) boats to this profile with outstanding results .... gives better LIFT properties to the keel. Of course any 'endplate' added will reduce the harmful tip vortices that come off any wing/keel .... but you already know about the 'beaver tail' Flat plates may give higher drag and cause secondary vortices ... flats were quite thoroughly investigated by NACA in the 1960s .... you can find this work in the compendium "Ancient Interface" a NACA sponsored project for the investigation of foils , etc. used in boats and hydrofoils. Most technical universities have (had) "AI" in their libraries. Additionally and alternately, anything you do to "fair the bottom" including SMOOTH bottom paint and folding/feathering prop, etc. will help as the keel and underwater surfaces are a 'system'. Anything that will reduce parasitic drag will affect a keels (wings) LIFTing ability. A long shoal draft keel obviously has a low aspect ratio L/D ... but obviously it can 'always' be improved w/r performance. The keel system 'balances' with the 'above water' foil system... and thats why I offered/suggested to also consider improvement of the 'reactions' in my original post. hope this helps.
be sure that the leading and trailing edge shapes of the keel and rudder are close to the NACA "010" shapes/profiles. The 010 profile is 'generic' keel shape probably used by most of todays 'good' boat designers. This shape will give you close to the best shape and efficiency. The NACA 010 (dont have the other prefixes and suffix numbers of the '010' ... went somthing like NACA64010xxxx? but is simply called the famous/reknown "010") is a foil shape used in aircraft AND boat keels/rudders. Just do a websearch for "NACA 010"+"KEEL" NACA was the predecessor of NASA. I've reshaped most of my (racing) boats to this profile with outstanding results .... gives better LIFT properties to the keel. Of course any 'endplate' added will reduce the harmful tip vortices that come off any wing/keel .... but you already know about the 'beaver tail' Flat plates may give higher drag and cause secondary vortices ... flats were quite thoroughly investigated by NACA in the 1960s .... you can find this work in the compendium "Ancient Interface" a NACA sponsored project for the investigation of foils , etc. used in boats and hydrofoils. Most technical universities have (had) "AI" in their libraries. Additionally and alternately, anything you do to "fair the bottom" including SMOOTH bottom paint and folding/feathering prop, etc. will help as the keel and underwater surfaces are a 'system'. Anything that will reduce parasitic drag will affect a keels (wings) LIFTing ability. A long shoal draft keel obviously has a low aspect ratio L/D ... but obviously it can 'always' be improved w/r performance. The keel system 'balances' with the 'above water' foil system... and thats why I offered/suggested to also consider improvement of the 'reactions' in my original post.
hope this helps.
It is what it is
I would think modifying the underside of your 39 would be an expensive proposition. If you have to have better windward performance, you are probably better off with a different boat. Not at all a swipe at your boat, it was desisgned and built to cruise, I would imagine, and probably does that well. One thing that may help would be to move your genoa tracks inboard if they are outboard of your shrouds.
I would think modifying the underside of your 39 would be an expensive proposition. If you have to have better windward performance, you are probably better off with a different boat. Not at all a swipe at your boat, it was desisgned and built to cruise, I would imagine, and probably does that well. One thing that may help would be to move your genoa tracks inboard if they are outboard of your shrouds.
Compromise
Rich, all, After spending some time looking into your references, reading al replies,I realised that a "cheap" improvement on a shallow keel does not exist. Mounting a flat plate in the correct angle would be messy. If well done it should increase pointing a little but I would loose speed. You know, I decided to be happy with what I have. A nice boat for shallow waters and fast sailing down wind. Thanks all.
Rich, all, After spending some time looking into your references, reading al replies,I realised that a "cheap" improvement on a shallow keel does not exist. Mounting a flat plate in the correct angle would be messy. If well done it should increase pointing a little but I would loose speed. You know, I decided to be happy with what I have. A nice boat for shallow waters and fast sailing down wind. Thanks all.
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