Converting sail to power

[Chick Marcoux]

I'm converting a 19 ft sailboat into a harbor launch. It has a stub keel, draws 19 inches, 6'9" beam, 1750 lbs. displacement and has a spade rudder. I will be using an 8hp, 4 cyc Yamaha long shaft (25"). The boat has a hull speed of about 5.5 kts. Is this motor adequate to move it at hull speed in a chop and, should I remove the rudder or fix the motor and use the rudder with shortened tiller?


Chick

[gonzo]

The power is adequate for hull speed. You can remove at least part of the keel to lighten up the boat. Outboards steer better than a rudder. Have you tried to float the boat with the motor on? Those diesels are very heavy and may make the boat squat. A typical solution is to install hobles. That is an addition on the aft end of the hull to straighten the buttock lines.

[sukibe]

I am in the same boat (no pun intended). I am converting a 22 foot sailboat into a repro of a 1929 cabin cruiser. I have cut off the existing cabin and plan to install a full headroom cabin, removed the existing cockpit benches and floor, plan to install a somewhat lower floor, no benches. The helm will be in the new cockpit with steering wheel, windshield and canvas on frame roof over the cockpit. I have removed the bolt on keel but am now having reservations as to how well the boat will track and what I should use for ballast as what I havve now is a rather large round bottomed canoe! I welcome any sugestions as to design. I plan to use a 9.9 Yamaha high thrust for power, any comments on that appreciated as well.

[gonzo]

A pair of bilge keels will give you shoal draft and stability.

[sukibe]

Thank you Gonzo, Could you explain bilge keels to me, sorry to sound ignorant. The sailboat I am modifying actually has no bilge. The floor of the cabin is actually the bottom of the boat. I did consider putting down a layer of poly film and pouring cement on the lowest point of the floor right over where the old keel was. What do you think?

[gonzo]

Bilge keels are twin keels. They also allow the boat to stay upright in low tide. Normally they are canted out some. That is, they are not vertical, but the lower part is further out than the upper. By the way, why did you remove the keel?

[sukibe]

I removed the keel because I was working towards a shallow draft boat. Since there would no longer be a 25 ft. mast and sail to counter balance I thought the keel was unnecessary, but feel the boat needs ballast and some kind of keel for tracking. I got the picture of the bilge keels now, thanks.
There was another consideration too for removing the keel and that was to lower the boat on it's traler to make it easier to launch.

[gonzo]

If you plan on inside ballast, adding scrap lead to the cement will make it more effective.

[sukibe]

I took a close look at my cast iron keel today and discovered that it is lead! Since it no longer needs to counterbalance a 25 foot mast I want to cut it down in size (depth) and thereby reduce the draft of the boat. Any clever ideas of how to cut lead. It is a split keel so most of it is only about 1 1/2 inches thick with the bow end about 4 or 5 inches thick. I want to melt the waste lead and use it to fill the space left by the removal of the swig keel.

[gonzo]

A circular saw will cut lead. Use an 18 thooth blade. Are you going to melt lead and put in the slot for ballast?

[sukibe]

Yes, that is my plan, any suggestions? I plan to bolt a piece of wood to the keel bolts, turn the keel over, stop up the open end and then fill the slot. I have to find some way to clean the inside of the slot as it has a lot of growth in it.
Grant

[gonzo]

Your boat will catch on fire if you pour molten lead into the slot. A method would be to cut slices of lead about the width of the slot and set them in resin. Finish the job with fiberglass on the bottom.

[sukibe]

I agree, except that I took the keel off the boat and it sits in the middle of my yard, so no danger, or not much if I am careful. I like the idea though of not melting the lead. I will give your idea some thought, should be a lot easier than melting the lead. Thanks. By the way, did they alloy another metal in with the lead to make it stronger?

[SailDesign]

sukibe, usually antimony is alloyed to increase strength.

[Willallison]

One aspect of all this that goes back to the original post and which has not yet been mentioned is that of thrust. I don't know about other o/b manufacturers, but Mercury produce a range of "high-thrust" props. These have very low pitch and a much greater blade area. We occaisionally fit one to a 15hp o/b on our tender - it will happily push / pull our 20+ ton 48 footer around.
May be worth considering for this application too....