repowering my sailboat- engine selection

[Chinook92]

hows it going?

so.... I have a Catalina 27, picked it up for 1000$ and have subsequently gutted it, replaced all the bulkheads, plumbing, and currently doing the systems. my boat is an outboard model, with the well in the stern, and I have a great 15hp Suzuki on the back, but, I would need to hack up the transom to get it to tilt up which I don't want to do. I started thinking how much nicer it would be if I found a small diesel to stuff in there, and have all the luxuries of a diesel engine (like hot water, and that any time any where diesel reliability), but most importantly a charging system for my battery bank.

that's probably no easy task for your average boater, however, I am indeed a marine diesel mechanic, and install, fix, maintain, and repower boats for a living, so, for me personally, glassing in some engine stringers and fiberglassing in a stern tube, and sealing off the transom really isn't a big deal to me. I work at a boatyard, and have every tool in the industry at my disposal, and my boat is even on the hard there, so, its a pretty sweet deal, and given what I have to work with, it seems like a no brainer to install a diesel


the boat is a 1979 Catalina 27 tall rig, which has a displacement of 6,850lbs, and a waterline length of 21.75 feet and simple math says that I have a hullspeed of around 6.5kts and that a diesel in the neighborhood of 12-16 horsepower is ideal

with all of that in mind, I am not planning on day sailing or beer can racing, while that may happen, the emphasis of my boat is to take a 1000$ junkyard POS boat and rebuild it to fit my needs to the industry standards....

kind of like how some guys take a rusty old car the found in the junkyard and rebuild it and customize it, I do that with boats, and have done it for years. gets me the most bang for my buck, and as far as my sailboats go, I can usually get in under 1$/mile once its in the water. makes boating affordable to me, and I usually make a killer profit

but this boat is different, I live in Washington state, out in the san juan islands, and have all of that great sailing right at my front door. on a Thursday night, I can even move my boat to the dock at work, so come Friday night once work is over, I can simply untie and take off for the weekend and tie up at the dock at work sunday night and be ready to go for Monday. beyond the San Juans we have BC and Alaska and that's where id like to go. ive done that trip several times on commercial fishing boats, but never in my own boat.

needless to say, the recommended horsepower rating for my boat, seems to be suggested for as the boat sits, with its base weight, and what im wondering is if by bumping the horsepower up to say 20hp of that would be more suited for a boat that will be carrying a 2 people, gear, and supplies for extended trips, and extra fuel, but most importantly, have that extra umph for fighting tides and currents

even locally we have tides that can get going 6,7,8 sometimes 9kts or more

we also aren't seasonal boaters, if I have a boat, it gets used year round, but that still has me wondering about a larger motor being underloaded. id hate to spend my hard earned cash on a motor to under load it and have it die prematurely because it simply wasn't used hard enough, and on the flipside, get an engine that will be over worked pushing a heavier (than your typical C27) boat in strong tides

there is reason why I put a 15hp outboard on the boat origionally, however if I recall those motor are rated for horsepower at some super high rpm number because of the torque curve, so while the boat had a factory option for the M18 universal diesel, which was 14hp, that torque is made at such a lower rpm. I think the recommended outboard motor for that boat was a 9.9 mainly because of the gearbox in the lower unit, but again, I also plan on going long distance.

if the factrory recommendation was 14hp, but plan on pushing a boat with a full load of gear for 2 people up Vancouver island, and potentially through the queen charlottes to the Dixon entrance or even staying in the protected waterways going north, would 6 more horsepower be bad?

sure there are other boats that have better equipment, best suited for the job. my boat aint no Gulf-32, but by Catalina standards, its going to be a tank when im done with it, and that's part of the fun of the project

id love some input to my motor selection