re powering

Discussion in 'Outboards' started by talau1978, Aug 26, 2016.

  1. talau1978
    Joined: Aug 2016
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    talau1978 Junior Member

    hello to all,

    I'm in the works to repower my BF 32 flybridge from inboard to outboard engines. I'm looking to repower with a twin evinrude 250 or 300 HP 30" shafts. can these engines perform on this hull. I like this idea because I've seen Bertram 31 FBC with outboard engines. as i can see with the BF the weight is more on the bow cabin,tower, least, but not the last are the heavier inboard engines she currently using besides fuel and water. I just want to know if this is doable? I hope I don't sacrifice fuel economy, but at the same time I'm not repowering to zip through, all I need is point A to point B and everything in between back from 10 to 30 miles out in one piece and still provide the torque and thrust when needed depending on conditions out at sea. feel free to point out how and what to see, expect and what can I do to improve this project, all opinions are welcome.

    thanks for all your inputs.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    What is your current setup? Converting to outboards is more complex than you might think. Often you need to move tankas, of course there's controls and linkages and lastly, is you transom able to cope with the weight and power of the outboards.
     
  3. talau1978
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    talau1978 Junior Member

    thank you Mr.PAR

    I'm gonna gut the whole BF and pretty much rearrange the tanks and reglass the cockpit and fortify stringers from hull to transom with divinycell beams to accommodate the outboards. this build will be more light compared to the original bow cabin/tower set up,,, this is gonna be out of the original footprint. more simple light and strong. I know the waterline will change and i have to be mindful on the building materials to make sure balance.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Ideally, you don't want your WL to change, nor your weight distribution. Light and strong is nice, but you need to keep the balance. What is the make, model and year of this boat? Was a single engine version available on this hull?

    If this is the boat I think it is, she's pretty heavy for her length, but this has some advantages, other than at the fuel dock. The major one is ride quality, compaired to say a Bertram 31, it feels like a rock in a rough slosh, while the lighter Bertram 31 is a bit corky. The BlackFin prefers to run in the low to mid 20's, so pushing her much faster will just eat into your pocket and once you get near 30, she'll start to plow, which progressively worsens as speeds rise.

    My point is, making the changes you currently envision are fine, though you should evaluate what you really want and need, as you just might get it. Are the 375's beat? That's a lot of iron to make up for.
     
  5. talau1978
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    talau1978 Junior Member

    its an 87 BF 32 flybridge,,, balance will be key and even though bow cabin and towers and inboard engines are a lot of weight to make up for I know the hull due to length and width is heavy enough to maintain a constant and easier weight distribution. The hull for this blackfin with gas is at a astounding 17,000 lbs (lots of weight),,, so the bow cabin/ tower, engines might make up 1/2 or 3/4 of it's total weight which I'm gonna remove and redo a different cabin lay out which will add weight too, but not as heavy as before, but I know the hull is heavy enough to counterbalance the power plant. Mr. Par thank u for ur insight and help on this matter and I know there is one thing talking in theory and there's DOING,,, to easy to talk!!! lol
     
  6. PAR
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    PAR Yacht Designer/Builder

    Those diesels weigh about 1,800 a each. Pulling this much weight, losing the flybridge and whatever else, plus shifting much of this weight aft to the transom will (not if) alter the boat's trim and these puppies are trim sensitive. At best, the outboards will be about 1/3 to half the weight of the diesels (about 600 pounds each), so this is a lot of additional fuel tanks and furniture to make up.
     
  7. talau1978
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    talau1978 Junior Member

    Yes that's what I'm concern with too, I know for sure the fuel tank have to be shifted and when I build the cabin that gives me the opportunity to use more heavy glass and wood other than expensive divinycell,,, 1800 lbs each(engines) is a lot to make up for in wood and glass, at the same time I don't want to be heavy towards the stern or towards the bow, so the only proper way to balance bow and stern, I have to do this in the water,,, engines mounted 3/4 tank or full mock tank not set in place and from there move the up(bow) or down(Stern) and make sure it's properly balanced and don't forget to factor the cabin. I want the weight to be from mid hull towards transom when floating or not in motion. basicly engines & fuel tank & cabin. Just the balance that i need to do this boat job. thank u again Mr. Par for ur insight and experience in this field and letting me know what to look for and factor into this project.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Is it currently twin diesels ? Why would you want to ditch that ?
     
  9. talau1978
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    talau1978 Junior Member

    they're in,,,but want something different I want more cabin real estate and with this hull it's so deep,,, possible aft cabin more to comfort and fishing offshore with the creature comfort of home and still keep the classic BF 32 hull look that was more known to be good dry ride, wave tamer and with all the bells and whistles. that's all I wanna do maybe minus the tower.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Big job, and it sounds to me that you would be better to change boats to something with more living space.
     
  11. talau1978
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    talau1978 Junior Member

    re power

    I don't wanna part ways with her she's been faithful and strong at trying times out there. I like her because she's so unassuming labeled to the common status quo, but when I'm done with her I know at least I gave my all. maybe why not upgrade? to me it's more the personal touches that matter to me sticking to a proven hull that has rival it's competition the B31 whose legend is all over the world, people call it a knock off,,, but to a knock off with the qualities you want when you get tossed out in rough water,,, beautiful PLATTFORM.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    I quite believe it is a good platform, more reason not to bugger around with it !
     
  13. talau1978
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    talau1978 Junior Member

    yes sir, its about time i redo this boat,,, thank u and Mr.Par for all the input on on balance power and so thanks guys been of info!!
     
  14. PAR
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    PAR Yacht Designer/Builder

    I've taken on projects like this previously and it's a lot of work. It's nearly impossible without some prior experence and not possible while the boat is in the water. In fact, not possible if the boat is on a trailer, unless very well supported (other than some bunks and rollers).

    Ideally, you'd put her on the hard and make a cradle to support her, knowing much of the structure will come out in time and you don't want her to distort, as you make changes. The cradle is usually nothing more than several athwart braces, that mimic the shape of the boat on fairly close centers along it's length. Plywood and 2x4's work well for this, with some longitudinals to keep things aligned. I usually make a pretty good estimate of her longitudinal CG at this point, as a reference for the remodel. Next is the gut out, which is how it sounds, you yank out everything that's going to be in the way or needs to be removed for some reason. Naturally, you weigh everything as it comes out and note its location, so you can approximate how much needs to go back in and most importantly, where it needs to live, so the boat will balance.

    With a gutted boat, you make a plan to fix what needs fixing, taking weights as you go, then any new stuff you've planned on, also noting weights and locations. This is the only way to insure it'll float where you hoped come re-launch day. Most of us will develop a spreadsheet to keep track of stuff, as it can get pretty anal and tedious without one. At some point you'll have a pretty good idea how you need to trim her up, which could simply be some ballast or shoving around some weights, like tanks and battery banks. The CG reference comes in real handy at this point, so you move things around or add trimming ballast until you're as close as you can get it.

    Again, unless you've done this sort of work before, it's not something the backyard builder can take on. This isn't to say you can't, but is just to say the odds of a completed project this scale is quite low, for the average guy. This isn't a summer project, in fact, a skilled guy, working in available off work hours will takes years.

    Check out Bart's thread (he has several application spicific ones too) about his 7 years remodel of an old Silvertron > http://www.boatdesign.net/forums/wooden-boat-building-restoration/old-boat-new-life-18865.html < This is typical and he started out as an modestly experenced, yet determined owner.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    What's to be gained from this, except engine boxes no longer getting in your road ? I don't understand it. And aside from anything else, the minimum effective cruise speed for those mega outboards is 25 knots at least, and ideally somewhat more, otherwise it is an inefficient set-up.
     
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