Adding a 3 foot transom outboard bracket

[irv]

Before I do this going to ask for a little advise from those who know what I don't. I have a 24' Fiberform that was a IOB OMC. My plan as I rebuild this with a 3' bracket on the back for twin 115 HP Evinrude outboards. Was a camper stye from the 70's and plan to remove the heavy top, the alaska bulkhead, heavy old camper stuff, add a canvas top and new lighter equipment so I could still live in it somewhat when in mexico after retirement. Running the fuel system from where it is in the center between the stringers, starting about 5 ft' forward of transom @ 50 gallens further up to where I'll have 125 to 150 gallens so that will add weight center to forward when full. Has anyone did a project like this or had experience with it? I am worried that the boat will run poorly do to the weight changes and angles with the 3 ft' outboard brackets. The boat was concidered a heavy built boat when new. HP of the 2 115 e-tecs about what I had when it was a IOB with a 302. Weight will be more with full fuel (guessing here). Center weight will grow a bit with fuel and fresh water tanks while rear weight should be less or same after live bait well installed. I'll take any help I can get. Thanks

 

[gonzo]

The short answer is: she will squat. You are taking a lot of weight from the front and adding extra weight on the back. Using fuel to balance a boat doesn't work, because as you use fuel the balance changes.

 

[irv]

So did some measureing this morning. Assuming the center line is the center of where the old gas tank is installed. I the weight I'll be adding will be forward of that the center line. Batteries could very easily be set forward along with the fresh water tank. With floatation from the brackets and addition of trim tabs you think the boat would squat while sitting or never trim properly when cruising. Been reading all forurms on this and its a bit confusing. The outboards weigh about 400 Lbs less than the old OMC drive. The old boat squated a bit when sitting bit trimed fine when planing without trim tabs as I nerver had them. If you think weight distrubition forward could adjust it. I could, after engines are installed, actually use rocks in boxes and buckets and simulate the weight of the equipment to see if it could be balanced. Is there a rule of thumb for refits like this as to how the bracket affect the weight distrubition. Seems some people just but one one and go and swear by it and a few say they had problems. Thanks for any help

 

[Bruce46]

Others have done similar power switches and have been happy with the results so there is a good chance for success. However there a a few things to keep in mind, such as where you place items such as tanks, batteries, etc. Tripling the fuel capacity could cause problems as that is a lot of extra weight. Moving the starting batteries forward is not a good idea as it could create starting problems.

If you haven't bought the engines I would suggest putting a larger single (250) and a 10 hp for trolling. You'd get about the same speed burn less fuel and a lot less weight out back. An absolute addition for crusing down south is the best fuel filters and you might want to think about a small water maker for drinking water.

Good luck.

 

[irv]

No, I haven't bought anything yet. I plan and plan first. The duel motor idea was for saftey. Am having second thoughts after reading the forums. Seems the new outboards don't break like they did. Checking into a water maker today. An AC unit in the cuddy cabin will use 70 amps at 12 volt. Might pass. Still very worried about breaking down far from anywhere. First step is actually rebuilding the boat. Stringers were replaced in 1995 but I didn't take good care last few years. Might be alot of work there. Thanks for your input. Any help is good help at this point

 

[gonzo]

The real question is: Why? What is the problem with the factory setup?

 

[irv]

The original set up was an OMC outdrive with a OMC 302. When I bought the boat it had the stringers replaced, spruced up in the cabin and a new 302 Ford industrial installed. The engine is still very new hour wise. Just been sitting. The outdrive is not new and do to age not worth messing with, least to me, plain wore out. Down in Baja, where I plan to spend 3 or 4 months a year help is far and inbetween. So, with that thought in mind, the dual engine concept for safety looked appealing. The range with the old 50 gallen tank will not allow me much travel distance. After reading through the forum, and listening to you, I'm also going to look into a new outdrive for the 302. Ecomomy, do the expected hours I'll be putting on is a point also. As I see your very experienced, relaibility, with safety, and fuel economy being last (wife would kill me if I disappeared down there) would you refit to dual outboards, one large outboard, one small, or go through the 302 (good with mechanical equipment) and mate it to a new outdrive with a small outboard as back up. Plan on going up most of the Baja side (Sea of Cortez) and just have a good time, living in boat 5/6 of the time, solo. Your statement about being but heavy put some worry on the dual outboard idea. Any thought will be highly regarded. Thanks.

 

[gonzo]

A small kicker for back up is a good idea. You can also use it for an inflatable dinghy. If you have a good engine, a rebuilt outdrive will be much cheaper than an outboard and bracket.

 

[irv]

THanks for all the infor, found out today youy can't buy a new outdrive period. Only complete combo's. So as I have time (rebuilding boat first) I'll start looking at that possibly, if not than shell out money for either duals or one large single and a small kicker. Seems cost is about the same either way. Thanks

 

[marshmat]

I tend to concur with Bruce that there won't be any advantage to twins in this case. The number one killer of outboards, by far, is crappy fuel- in which case both engines die within a minute or two of each other. Your boat won't be able to plane with one off-centre 115hp, so you'd be stuck at five knots anyway when running on one engine. You may as well use a larger single main engine (one 250 is lighter and more efficient, all told, than two 125s) and mount an off-centre 10-15 hp kicker with completely independent fuel and electrical systems.

Any outboard-on-bracket solution is going to shift the boat's centre of gravity aft, relative to the current setup. It's likely she'd squat more when coming up on plane, but perform better at top speed. Not a good trade-off, IMHO, as most boaters tend to cruise at the low end of the planing speed range.

The Ford 302 is a popular engine; parts seem pretty easy to find (along with mechanics who are familiar with it). Giving it a new or rebuilt outdrive would be my preferred option. Avoid the old OMCs; pick something that's currently in production so that you can find parts for it in another ten years (I'd look at a Volvo DPS or OceanX, Merc Bravo 3, or if you want something really beefy, a Konrad). A kicker outboard would again be fair game, and could come in handy- remembering, of course, that it needs its own independent fuel and electrical systems to be useful as an emergency engine.

Since you're doing all this rebuilding anyway, give the engine bay watertight bulkheads and the biggest emergency bilge pump you can find, just in case any hoses, bellows or seals fail at some time in the future. (This does mean adding yet another bilge pump, forward of the engine bay, but they're cheap and do wonders for peace-of-mind.)

 

[irv]

Well thank you very much, been on the phone this morning and have completely made up my mind on what I'm going to do. My engine sits on 4X4slave stringers inside my middle 12" stringers. Engine can be tilted or moved forward very easy. Behind the engine I'm going to mount a Borg Warner 1X1 gearbox with trans cooler. Mount a Konrad outdrive to that. Just run exhaust out the back Like an inboard. Can use my existing manifolds, fresh water cooling, etc. Konrad figured with my 240 HP 302, the gearboxes have no expected life as they will be so under loaded. Saftey there. Total cost will be about $16,000. Weight about same as with outdrive. Simple steering from inside boat. No computers, no fuel problems from high tech, and engine is completely repairable in mexico if necessary. Thank you guys so much, went from a redesign to a bullet proof build. Never heard of Konrad but if the military and commercial guys use it, I'm in. Plus as he stated, if you can rebuild OMC gearboxes, this one will be a piece of cake. Thanks again for the help this far, now to start the work. Craig