Outboard Well Large Boat

Discussion in 'Boat Design' started by schuh, Oct 26, 2013.


What do you think about this project?

  1. Your Insane

    0 vote(s)
  2. Might Work

    0 vote(s)
  3. It will work but you will have problems

    0 vote(s)
  4. Sounds like a fun/feasible project

  1. schuh
    Joined: Oct 2013
    Posts: 5
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    Location: Panama City, Fl

    schuh Junior Member


    I'm new to the forum (but and old boater and livaboard) and would like some input on an idea i have.

    I am fortunate to have a home on a bay in the Florida panhandle. I have a nice water view but I would love to have a boat moored out front as I love looking at a moored boat.

    I need to do this on the cheap so here's the idea. i would like to pick up a older 25 -30 ft cabin cruiser with a bad or no engine. Glass over any holes in thr transom that were there for the IO. If its inboard, so much the better. I can get a hull like this for about $500.

    Then I'll build a well where the motor was about 18" by 3 ft.. The idea is to install a (approx) 25 HP outboard and run the boat at hull speed. The well would have a cover that would fit snuggly around the outboard to prevent any spashover. The outboards cavitation plate would be level with the bottom of the hull in the down position and would be able to be tilted up so the foot is out of the water and not subject to marine growth.

    The boat would only be used for short trips in the bay which seldom sees waves over 1 ft. Worst ever at the mooring would be 3ft, but obviously the boat won't be used in that kind of weather.

    I like some opinions as to the feasibility of my little project, especially how well the outboard/well combination would work. Would 3/4" plywood work for the well (glassed and epoxyed both sides)? All I'm looking for is 6 knots or so.
  2. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    Feasible. 3/4" ply and glass will be fine, triple up for the back side the motor will clamp to. Tie into stringers, bulkheads, transom, any major structure, us a few knees here and there. Forget sealing the top, the exhaust will have no where to go and remember you are dealing with carbon monoxide here, very dangerous.

    Steering and throttle may be problematic, unless you find an inboard and then you can keep the rudder and steering. For what you want throttle and shift can be on the motor, it will just mean planning any docking or mooring.

    Just glassing up all the "holes" will not keep the boat from collecting water. Don't care what kind of boat, you will need some pumps (YOU WILL NEED PUMP(s) and a way to keep a battery charged, maybe solar.


    Attached Files:

  3. Tad
    Joined: Mar 2002
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    Location: Flattop Islands

    Tad Boat Designer

    Are you planning on leaving the dead engine intact? If not there may be trim problems (solvable with ballast).

    You may find the motor (Even XXL shaft) will be too deeply immersed to tilt out of the water completely. Big boats draw more than little boats.
  4. boatbuilder41
    Joined: Feb 2013
    Posts: 162
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    Location: panama city florida

    boatbuilder41 Senior Member

    it will work. i have built many of well boats. some with the well in bow. some with well in stern. i even built one 30 foot with well in the bow with volvo stern drive and big block chevrolet motor. proper weight distrabution is critical to a well boats performance. well boats also perform better with tunnels exiting from aft of well to stern of boat. usally about 4 to 6 inches in depth. a well im the stern typically are open the full height of the well all the way out the stern. best bet is to install a bulkhead all the way across boat. this is to be used as the front of the well. well also needs to be wide enough that you can turn the motor from side to side under half trimmed position. also istall the bulkhead with a 15 degree tilt toward the stern. with the typical 25 hp motor....... you are gonna be restricted to 20 inch exhaust housing on motor. that means you cant make your well no more than 20 inches from the bottom of boat to the top of well.and this would be a long shaft. the most comon 25hp motor is only 15 inches.
  5. schuh
    Joined: Oct 2013
    Posts: 5
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Panama City, Fl

    schuh Junior Member


    No, Any engine will be pulled and outdrive removed (if its IO) The outboard well will probably go where the old inboard engine was. I'm thinking if I can find a hull that's essentially flat bottom (or nearly at the stern), it shouldn't draw more than 10" or so with the motor removed. Our old 42 ft Hatteras only drew about 1 ft if you didn't count props, struts and rudders.

    Boatbuilder 41

    Some good ideas there, thanks for the input. You've hit on my main concern ... with a short shaft motor placed with the cavatation plate level with the hull botton there will be only about 10 inches of freeboard in the well - I'm not real comfortable with that. A snug fitting well cover would help while under way but at anchor the motor would be tilted up to prevent marine growth and it would be hard to fit a cover ( in the unlikely case of rough water while at anchor).

    This is the weak spot in my plan - back to the drawing board!

  6. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    schuh. You'd be amazed how little sill is really required above the waterline. The bottom of the hull really dampens out the pressure signatures. There are sailboats that have barely four inches of freeboard to their well. One I'm familiar with was 30' and had a 40 hp in the well, which was in the middle of two quarter berths in the aft cabin and open to the entire boat. It happily came through many hurricanes in the Florida bay year after year. I ended up owning the boat for ten days, but knew of it for several years before that.

    I'd mount the OB on it's own sill and have a separate, taller, bulkhead to provide watertightness. This gets the prop a little lower, which is important for displacement speeds. You can mount the motor so that the powerhead is only inches above the waterline and get the cavitation plate as low as you can. Just to repeat - this is a setup for slow travel, once you have a planing boat, you don't need or want to do this.

    I just posted a photo of one of my old sailboat's ob leg on another thread. Not the one with the four inch freeboard, this one has a bulkhead. Notice the protrusion. The ob clamp basically bottoms out on the hull bottom and the well is located right at the waterline


    I'd look for old Shamrocks, Parkers, Gradys, Stamas's from the 60's-70's. But it would be cheaper just to find one with a working motor. A friend on mine bought one of these in working order for the price of a 25hp Yamaha. It had twin volvo penta douprops, electronics, radar, and complete canvas enclosures. I think he put a new mattress in it and the ac died after a year.


    You should be charging the owner to haul away a boat with a broken motor still installed. If it is a freebie, make them pull the old motor before you take it.
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