Winged keels

[davideso37]

In a previous thread there was discussion on keel replacement to improve the performance. One suggestion was to put a spacer between the keel and the hull to lower bulb. After discussing all options with a naval architect we have opted to add winglets to the bulb to try to achieve a similar result.
For background our yacht is a Sun Odyssey 37 but we have upgraded the rig with a 1.7 m taller mast and 0.56 longer boom. This has helped our light air performance and we carry 300 kg of chain in the bilge to improve the heavy air performance. In my opinion we are still not as quick as a Sun Fast 37 which has a slightly deeper lead ballast keel which has less drag.
The purpose of the keel winglets is to reduce the form drag on the very well designed but quite large cast iron bulb and to provide more leeway resistance so we can lean more and get to use our larger sail area.
The project has taken quite some time, firstly for the naval architect to design it and then for me to make a mould for the fibreglass winglets and do the fabrication. In the meantime we decided to upgrade the keel floor structure, not because it was required but because of reports of several upgrades on Sun Fast 37s. We have taken a very conservative approach and added an extra three full size fabricated glass floors of the same dimension as the original three floors, thickened the hull in the floor area and added two more keel bolts. Every keel bolt backing plate now has a floor on both sides. As a result we have doubled the keel floors and doubled the shear area of the backing plates. All this was done in consultation with the naval architect who shares similar views on conservative design of keel attachments.
Today we finally attached to wings to the bulb and next week we will start to see if the journey has been worth the effort.

We do not have grand expectations from the modification but will be satisfied if we can get a 2% improvement in speed around the course in 15 kts of breeze. Under this the extra wetted surface may be a drawback but it is supposed to be offset by the reduced form drag. I have a good record of results against a cohort of competitors and will not make any claims until after we have had a season to experience all conditions.
In the picture you can still see the construction tabs around the edge of the bulb moulding. These will be removed once the two halves are glassed together.
The alternative to the winglets on the bulb would have been a 2.4 metre draft new keel with lead bulb but I could do all the fibreglass work myself at a much lower cost than a new keel and it has been an interesting and entertaining project not only for myself but for the whole crew.

[MalcolmP]

Hi David

This looks fascinating and very appropriate that another Australian is resurrecting the Ben Lexcen wings. Your fibreglass skills look impressive too

Would love to see some more photos, esp before and after etc - presume the one shown above is when you first bolted the glass wings on and the joint has yet to be faired etc (oops - ignore just reread your post and note you say the tabs have yet to be removed)

Also if you have any pictures/notes of the keel bolt reinforcement process - did you do that all with the keel in situ or did the was the keel taken off etc, did you drill and tap the cast iron?

Will this impact on your rating handicap?

Do tell us more ;-)

Malcolm

[davideso37]

Malcolm,

We race to a performance handicap system so hopefully it will affect our handicap by the 2% I am hoping to achieve. It is not a lot but it will take us to the middle of the winter fleet on time. I am expecting the yacht to point a little higher which will be useful tactically as we are probably the lowest pointing yacht in our fleet.
In our summer twilight racing our main competitor is a 39ip and we tend to share the fastest times but I want a bigger share of the fastest times. The prize for that is to get back to the club in time to get a good table at the post race barbecue and presentation.
The wings are mostly vinyl ester resin with tooling resin chopped strand mix for filling the void between the high specification faces. They weigh 22 kg each which is a weight we could handle without resorting to mechanical lifts. The wings have a 2.5 degree downwards attack angle and a 9 degree dihedral angle designed so that the wing tips do not go below the base of the bulb.
As far as resurrecting Ben Lexcan's ideas, they have never died particularly with the shallow draft fleets in Europe and the USA. The shoal draft Jeanneau 379 has a nice large bulb wing combination and I would love to hear from anyone with one of these on their performance relative to the standard draft model.
Re the keel floors I do have lots of photos and full calculations and documentation in case any future owner wants to do category 1 or 2 races. Technically it was not needed as the hull is the same as the Sun Fast 37 which has a 200 kg heavier keel but as I said in the post I am particularly conservative and safety conscious as my whole family will tell you. It is not a job for the amateur as the plywood sub floor has to be removed and reinstated to get access to the floor. I did all the glassing on the water with plenty of ventilation and a full face fume mask. We lifted the boat onto the hard stand to drill and tap the two extra keel bolts. The keel hull join was and still is water tight so in hindsight I could have done it on the water but it was more comfortable on land. It took a full day to drill and tap the two holes 75 mm deep into the cast iron. The casting was amazingly good quality and I am continually impressed with the standard of gear on our Sun Odyssey 37

[davideso37]

Photo from the finished project

[krawall]

Dear David,

have you sailed with your wings yet?

Really curious about the outcome especially on a beat.

Cheers,

Tom

[davideso37]

Tom,
We have raced a few times but mainly in drift conditions where the wings are not a real benefit. The one breezy race we have had we reached past a yacht we rarely beat so we are optimistic that we will get the couple of minutes improvement we expect. We will need a full season to make a realistic evaluation and will see how our handicap sits at the end of 12 months.
What is immediately evident is how much less the boat rolls in waves as the wings act as effective. It is more noticable under motor than on the mooring so I guess there is some dynamic stability in the downwards attack angle as well as the area at play.
Regards
David

[so40gtb]

Very, very cool! Though I have a full-draft SO40, I do wonder whether similar winglets would benefit stability and overall performance, given the large size of the bulb at the bottom of our keel.

[davideso37]

Compared to the SO37 the SO40 has a higher ballast to displacement so the benefit may not be as great. The SO40 has a similar ballast to displacement ratio to the Sun Fast 37 and if I had the extra 200 kg of ballast on the end of my keel that the SF37 has compared to the SO37 then I might not have added the wings.
It is early days yet and I will not draw any conclusions until after a season of sailing. At this stage we do appear to be faster and higher to windward and doing relatively better in stronger winds where the wings add some dynamic stability.

Regards
David

[davideso37]

A few more races have gone by and we have also lifted and inspected the wings.

Wings are in pristine condition and now look like they were always meant to be on the yacht. We get many complimentary comments from passing racing sailors so at least they look good.

Upwind performance has been very good so much so that I have taken 200 kg of chain ballast out of the bilges to try racing for a while as light as possible. Downwind in a drift we are certainly no quicker and might even be a little slower but overall our handicap has come down around 2% and we are still learning how to sail with the wings.

Regards

David

[alenka]

A very impressive looking modification.  I hope all your hard work pays dividends.

Our previous boat was a Hunter Legend 290 complete with factory fitted winged keel - not that the wings were very big.  Never-the-less for a little boat is was very quick and we constantly gave our neighbour, a 40ft Benne, more than a good run for the money.  Alas, the downside was that Hunter made the boat shallow draft so she was very prone to gusts and more than a bit tippy in a blow.

Of course the big downside to a wing keel is that if you ever touch the bottom, even soft mud, you are probably going to get stuck and need to be towed off.

[davideso37]

A year has gone since the last comments so thanks for the anniversary comments. We are still very pleased with the modification particularly in fresher conditions when we are down to a No 2 or 3 headsail but we have also had some good results in light conditions. Luckily we have not hit bottom yet but the plan is to keep the boat flat and back out under motor. The wings are angled down so going forward would be like dragging an anchor.

Regards

David