replacing keels with daggerboards

[colemj]

Hi Gramos,

Wow, that's quite ambitious and I applaud your courageous thinking. First thing I would do is attempt to contact Erik Lerouge and ask his opinion or pay him for engineering designs. I would think engineering advice to be very important because daggerboards will add forces to the hull and changes in the distribution of forces across the boat structure that weren't accounted for in the original design. Also, placement of the boards with respect to centers of effort, momentum, etc would seem to be a critical parameter. Are your keels integral or sacrificial? If the latter, that might make the conversion easier.

Actually, the first thing I would do is rethink what/why the change? Keep in mind that some basic speed-related parameters are already baked in the cake and won't be changed by daggerboards. These include hull length/beam ratio, weight of boat, bridgedeck clearance and underbody shape, sail area and sail plan, etc.

Also, consider that your rudder is part of the draft, so you might not gain the advantage of the full depth of the keel in draft reduction.

I don't know of the Sunstream 38. I have seen a 32. Do you have a picture you could post (mostly for my curiosity - not for answering your question)? If it is a Lerouge design at that length, it might be similar to my Manta 40.

Mark

[Joli]

I would think pre-maiking the cassettes with a flanged top would make the install job fairly quick and easy. Maybe the factory already has them availaible?

[44'cruisingcat]

Originally Posted by fhrussell

Gramos,
I would first contact Eric Lerouge:

Erik Lerouge Yacht Designs

Here's and interesting article as well:

Articles - Daggerboards

Good article , thanks for that.

[Pat Ross]

I am curious as to why you would not sell that boat and purchase one that is designed with the features you like?

[Tnflakbait]

Originally Posted by Pat Ross

I am curious as to why you would not sell that boat and purchase one that is designed with the features you like?

This daggerboard project sounds like it could be too much work... But that sounds like more work to me!

It's really not too hard, but you must have a plan and know what you are doing. I would first pre-build the daggerboard boxes. Use Glassed plywood or foam for the sides. Use some very durable material for the front and back of the boxes. Fiberglass works well.
cut off the keels, and fair off the place where they were cut.

Cut a slot in the deck... Cut a slot where the dagger comes out...
Slide trunk in and glass it well. The daggerboard should come out underwater at the center of effort of your old keel. (If it is perpendicular to the waterline).

Good luck!

[David M]

You are getting into territory where you need to be consulting with a naval architect.

1. Any structural mistakes can sink your boat endangering life.

2. Do you have all the knowledge necessary to predict the performance increase vs the cost? No offense, but it is doubtful, otherwise you would not be asking the question.

3. Having someone else design the modification keeps you from being the responsible party if this major hull modification does not work as anticipated and all the money you spent on it goes to waste.

4. Is your insurance company alright with an amateur major modification to the hull?

[Therapy]

Originally Posted by rickm505

I think I have two Geminis saved on this computer.

Gemini is on my list of maybe boats. Small though.
It takes a trip through the boat to raise a board.
Could I see those please?

[luski]

I think a job of this complexity is best left to the profesionals, if you really want to make your boat point better and sail faster you should buy a set of really good sails ,fair the bottom, and take as much junk off your boat as possible if this fails to live upto your dreams sell it and buy another boat. more suited to your needs.

[Keegan]

DONT DO IT!

[cat man do]

Geez. here was me thinking cutting keels of and putting boards in was no big deal.

Easier than cutting boats in half and adding 5 feet to the length in the middle

Easier than cutting the bows off back to the mast B/H and making longer, more bouyant bows.

Easier than cutting deck and cabin off and putting a new one on.

Its only a couple of boards and keel removal.

For what its worth,
make the boards first,
wrap in corflute about 3mm thick,
glass around corflute,
make sure you can still slide board out of corflute,
add chosen core material to glass,
fair and glass core,
slide board out,
get rid of corflute.

Now you have a close fitting daggerboard case matched to the board.

Dave

[44'cruisingcat]

Exactly Dave. I used bubble wrap and covered that with peelply, instead of corflute, but same principal. It ought to be a weeks work. Two at the outside. BUT, he needs professional advice on what size boards, and where to position them.

[cat man do]

Originally Posted by 44'cruisingcat

BUT, he needs professional advice on what size boards, and where to position them.

Absolutely

Dave

[fastcat435]

I would think a bit longer before taking on that chore
We buyilt the fastcat 435 with both high aspect ratio mini keels and optionally
lets first give you the possible advantages.
1.Slightly higher pointing 2 to 4 degrees
2.Less draft ( but you rudder or saildrive will hit the bottom first)
3.Maybe a higher speed downwind.

The definate disadvantages
1. more weight in case of the FastCat 435 400 kilo,s
2. less space in the boat
3. more work to sail your boat.
4. higher chance of damage , catana builds extra daggerboard for each boat they build
5. higher cost and you might ruin a good boat if the job is not done professionally
6. The possible advantages will only really work if you have performance type hulls or a waterline lenght to widht ratio of 1:10 or better

[Pat Ross]

Have you thought of using something like the TomCat 9.7?

[2Hulls]

Originally Posted by fastcat435

4. higher chance of damage, catana builds extra daggerboard for each boat they build

Wonder where they put mine?

Originally Posted by fastcat435

3. more work to sail your boat.

Sounds like you're rationalizing now. "More work" is simply gravity for down and cranking a little on a winch for up.

It appears pretty clear that the serious sailing cats have boards. Mini keels also clearly have a few advantages - especially after you make the compromise that you don't care to have a serious sailing cat.

Dave