Conversion to Keelboat

rlltrash · #1 07-29-2012

How easy or difficult is it to convert a centerboard dinghy (16'-20') to a keelboat with a lifting, or drop, keel or a swing keel? Are there any boats that are better than others for this type of conversion? I have seen Capri 14's with a keel and I think there are others.

I am thinking of a bulb keel like the Viper 640 and VX One. A fixed keel will not work. The objective, of course, is to improve boat stability with varying crew weights and wind conditions.

Any ideas?

Richard

Stumble · #2 07-30-2012

Richard,

It would be very dependent on the boat, but on most boats it would be a major refit.

Building a new keel would be easy, sliding it into the slot wouldn't take much. Reinforcing the daggerboard trunk to handle the loads however would be a major undertaking.

Figure the VX keel applies a maximum static righting moment of around 600 foot pounds of preassure to the hull. Which is carried by a relatively small plate. And then distributed to the rest of the boat. The scantlings in this area are some of the thickest in the boat to absorb and disperse this amount of load.

To add this to a boat not designed for it, would likely result in having to completely remove the current sump, reinforce the floor, possibly add a stringer, ect...

rlltrash · #3 07-30-2012

Quote:

Originally Posted by Stumble

Richard,

It would be very dependent on the boat, but on most boats it would be a major refit.

Building a new keel would be easy, sliding it into the slot wouldn't take much. Reinforcing the daggerboard trunk to handle the loads however would be a major undertaking.

Thanks for clarifying the matter Greg. That is exactly what I am concerned about. Are there any other boats that are built for optional keels - like the Capri 14? Or, do any gear manufacturers make some kind of reinforcing kit for such a conversion? I could not find anything on the internet, which is why I am asking.

What happens to the centerboard trunk when a boat capsizes and the crew climb onto the centerboard to right it?

Does anyone have any other thoughts?

Thanks, Richard

SchwarckT · #4 08-01-2012

I added lead ballast(115 lbs)along both sides and in front of the centerboard trunck in my 15' daysailer to improve stability. It made a big difference.

rlltrash · #5 08-01-2012

Quote:

Originally Posted by SchwarckT

I added lead ballast(115 lbs)along both sides and in front of the centerboard trunck in my 15' daysailer to improve stability. It made a big difference.

Tom;

That sounds interesting. Did you do anything to the centerboard itself or just add the ballast inside the boat around the CB trunk? (Some boats, like the Lightning, have heavy weighted centerboards.) Is the ballast removable for occasions when you want to take several adults sailing? Do you notice the difference more when the boat is still, not as tippy, or in motion, less hiking?

Richard

WDS123 · #6 08-01-2012

The Lido 14 and Harbor 14 are made from same hull and deck molds.

If you are from the OC you should see zillions of Lidos and Harbors around.

If you want to convert an existing Lido 14 to a Harbor 14 - it can be done with a sawzall, putty, lots and lots of gelcoat, plus a huge amount of elbow grease, and you'll need 250 lbs of lead for the keel.

wdschock.com

If you want a lifting keel - our parts depart. could one for you from an existing sportboat lifting keel approx. 60" depth, 400 lbs bulb, carbon fibre, epoxy and vinlyester, high aspect ratio - but when you hear the price (lead is expensive) - you'll quickly forget the project.

SchwarckT · #7 08-01-2012

The lead blocks are permanently fixed in place with polyester resin(Bondo Glass). I didn't do anything to the centerboard(metal alloy). The increased stability is noticeable at the dock and under sail. Before, the boat was very tender. Now it behaves more like a "real" sailboat. I got the idea from my O-Day Mariner which has internal ballast along the sides of the centerboard trunk.

peterchech · #8 08-02-2012

RE: a lifting bulb keel on an 18' boat http://www.google.com/url?sa=t&rct=j...5oKeQzBsEWSOXg

I have built a few small sailboats, nothing professional but I do have an idea as to what is involved. IMHO building the foil and bulb is the hardest part, but certainly not outside the abilities of a novice. Google i-550 sportboat keel and there will be lots of posts of people doing this exact process. Reinforcing the case for the lifting keel should be much easier. It will require at least one bulkhead at the leading edge to distribute the load out to the gunwhales. Then reinforce the floor /case joint with a couple layers of glass and maybe a grid. The loads will be significant, but can be calculated so don't go overboard here. A properly glassed in bulkhead is very very strong, much stronger and lighter than just overbuilding the whole thing with 2 million layers of glass and plywood. Think load paths. If you can get your hands on the plans for a small sport keelboat like the i-550 you will see what kind of reinforcement is designed in by professional NA's and if the boat is of similar displacement etc you may be able to use that as a guideline.

Couple other things. Make sure you have enough flotation with the additional lead so if you broach you will be able to bail. Don't overload the boat either. Boatdesign.net is a great forum to ask this question, those guys might even help you calculate how much lead to put how far down. And it has probably been done before and posted there with pics.

peterchech · #9 08-02-2012

This might help too, a time lapse video will show you how the keel case is installed and what kind of reinforcement is used:
http://www.google.com/url?sa=t&rct=j...JuIWRX7yODE7qQ

rlltrash · #10 08-02-2012

Thank you for the above four replies. I was just going to ask Tom how he determined how much lead to put in his boat and where to put it (fore and aft.) The next two replies (peterchech) address those questions. I suspect a drop keel or weighted centerboard would have a similar effect, probably with less total additional weight.

WDS123, will the process you describe also work on boats a little larger? I am looking more at 16'-20' boats. By the way, Tom, what kind of boat is your 15' daysailer? Would you do anything differently if you were to do it again?

Are there any other suggestions from anyone?

Richard