Here's the substance of email's Brian & I had over motors and propulsion system, arguments for and agin.
Just another decision to be sorted....
From Brian:
Without weights of the components, I can't model the CG very well, especially on your version of the boat... but I'm going to guess that the closer the motor can get to the transom, the better. For propeller shaft angle, this isn't as good, but you do need to keep the CG in the right envelope so you don't create a boat that tends to bow-steer (CG too far forward) or porpoise (CG too far aft), and you'd prefer to keep the decks self-bailing, e.g. the boat, while at rest, trims slightly bow-up ...say 1-1/2" to 2" high at the bow for your boat length. If there is a risk of this not being true, consider compensating by slanting the decks downward toward the stern so water will drain out when nobody's aboard and the boat is docked in the rain. You would add long tapered spacers on top of the main stringers to do this, install them, then fit the web stringers and below-decks web bulkheads to this new run of the deck.
So ...I'm curious. Why an inboard? I understand avoiding issues with the leg on a sterndrive, and wanting better fuel economy than an outboard gives ...but does an inboard with its downward cant to the propeller shaft give better mileage? Its line of thrust would seem to be a bit less than optimal. And you don't get steerage without being underway, and pretty much zero steerage in reverse. I'm curious why you want the inboard ...what are the advantages? If the inboard has the economy of the sterndrive, then I get it... but if not, then hmmmm?
Thx,
Brian
From Ed
Well, Brian, I don't like outboards for a few reasons, on this boat, Petrol, not keen in the boat, taking a wopping 1/3 of the duck board space, batteries - how can the O/B charge all those, I will have on board, (ex - airline batteries, they're sealed and light.) now here's a rider, there will only be enough to cover the amperage I will use, solar panels to top up when at rest. Aircon & diesel heater, I can run this off the diesel, for those times of inclement weather.
There is here a nice place to 'drive' too, but it's 800 klm north, then while there why not go see Coral Bay - a further 1800 km north, hence the big tankage and diesel donk.
Auto pilot and GPS along with coffee's will be a nice crusie trip. looking at a 3 month trip.
The downwards cant on the prop I find an issue too, what to do?
The V drive ($5k) is 12 deg, the donk will be bolted as far back as possible allowing a little room to service stuff 'tween it and the transom.
Water ballast tanks are an option and will be allowed for in the build. So if needed I can plumb them up later.
Ed
From Brian
Oh yeah …diesel gets better mileage. A sterndrive would get better than the V-drive inboard, no?
I’ll try to model your boat for you, but it’ll be a bit before I can get to it and I’ll have to make some estimates …it won’t be exact (of course, it never is, right?)
Brian
Ed's revelation!
ok, so, there's 5k for the V drive, another 3k for the rest to the prop incl rudder, even say up to 10k for it all, that's enough to get a reasonable stern drive..... Oi like it.....
Ed
