Inboard Power Configuration

Discussion in 'Inboards' started by majorm, Apr 19, 2012.

  1. majorm
    Joined: Apr 2012
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    Location: South Carolina, USA

    majorm Junior Member

    I have a 28 Bertram that we have had out of the water for a few years without power. The engines we have but never installed just don't quite cut it power wise. ~ 150 Hp Cummins 4bt's and the boat weighs about 12,000 lbs with a deep V hull. So Ive accepted that the engines need to be sold off probably if i want to see over a 20 mph (~17 knots). So thinking inside and outside of the box what are some options you see? A few people have run outboard on this boat and with the weight reduction and center of gravity shifted they get close to 50 mph top end. I however don't really care for how that looks or want the gas bill.

    I have considered going back to gas like the boat originally had and considered other propulsion options. If i did some fiberglass work we could probably fit a Cummins 6bt in there but it may put the shaft angle too steep to get props to fit. I've read bad things about tunnels so i don't really want to venture there. Another option is a V drive. Ive see the dual propped outboards. Has any testing been done on using dual smaller shaft driven props on one shaft? That combined with the V drive would be an interesting setup if it were reliable. At one point the boat was sold with sterndrives as well but I don't know how handing or reliability would be with that.

    Anyway would some of you throw out some ideas to consider and discuss? This boat is also a dual inboard so it would be two inboards in the picture.
     
  2. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    Repower with gas as original, the B28 is a great boat the way it was designed. Unless you want to fund a Yanmar repower, thats your best bet.

    Are you familiar with the B28 site? i can't find the link right now but I did find this:

    http://www.bertram28.com/

    They also see a fair amount of talk at the B31 site about 28"s

    http://www.bertram31.com/bert31_fs.htm

    Your question about the 28 repower as well as the 31 is one that has been debated hundreds of times on dozens of boards, do a search.

    Steve :cool:
     
  3. majorm
    Joined: Apr 2012
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    Location: South Carolina, USA

    majorm Junior Member

    The 28 forum doesnt get much activity but im a member over at the 31 board and there are some great guys there with tons of knowledge. They have helped me as well as other posts all over the net as you mentioned. I was looking for something that may be a little different than the norm if it may yield better results than the tried and true. That's what I was getting at with including outside the box. Like you said the Yanmars are a good option but are expensive.

    The outboards seem to have great performance so thats what got me thinking about the outdrive. Albermarle uses this type setup on some of their boats. http://www.albemarleboats.com/trailerable/jps.html I dont however know how well the handle in slow speed and docking.
     
  4. keysdisease
    Joined: Mar 2006
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    Location: South Florida USA

    keysdisease Senior Member

    I/O should provide excellent slow speed handling and much better docking than convention inboard strut / prop drive. I/O just like outboard has vectored thrust which will be much more responsive than shaft inboard to steering input.

    The downside is: the additional cost of the I/O, maybe a jack shaft, maybe a gear box adapter, different mounts, fiberglass work, filling in the shaft box and strut holes, reinforcing the transom for thrust, etc.

    About the only long term upside of I/O would be shallower draft, and that not by much on a 28 twin engine inboard configuration.

    Putting in new or rebuilt gassers will be the cheapest and easiest by far with no worries about how the boat will perform. Any diesel option will probably never pay for itself in your lifetime.

    "Out of the box" by nature is experimental and usually expensive because you often have to invent sfuff as you go along. This will also cut into the value of owning a classic, restored with either gas or diesel, rather than a classic with a ******* drive train.

    Personally, I prefer to go boating. Steve:cool:



     
  5. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    It is not easy to power a smallish 28' boat with a twin and get 20+ mph. Hard to make it all fit. I have seen some smaller boat with a single diesel do it. The B28 was not setup for a single engine and draft would suffer. Consider that for fishing a outboard is not the best. Outboard best for going fast.
     
  6. majorm
    Joined: Apr 2012
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    Location: South Carolina, USA

    majorm Junior Member

    Is there such a thing as a counter rotating shaft driven prop using the same theory as the VOLVO Duoprop? By shaft driven i mean in what ill call a standard inboard configuration where you have shafts, struts, props and the rudders. I wonder if thats too long of a distance to have a hollow shaft with another solid one inside it and how it would be sealed? If that was the case a two or three bladed prop could possibly be used if it would fall in the optimum max rpm range.

    If i did use the diesels and putt aound we have to use a 4 bladed prop for it to fit. That is unless we go back to gas and then we could go 3 blades. After reading a good bit more on the outdrives it looks like they are a maintenance headache especially in salt water, which is where ill be.
     
  7. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    I should have mentioned maintenence, reliability and lifespan when I was talking about I/O's. Against a conventional inboard the I/O loses, as well as the power loss from the 180 degrees of power transmission.

    I am not aware of a dual prop conventional inboard system available for a boat as small as the B28. There is additional maintenence and complexity factors if there was as well as higher initial cost, and the propeller setups in dual prop installations are very sensetive.

    Write a check for a couple of Yanmars or put a pair of small block gassers in there and go boating. Either will enhance the value of a fine classic, anything else is a gamble regarding value and reliability.

    Steve :cool:
     
  8. Carteret
    Joined: Jan 2004
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    Location: Eastern NC

    Carteret Senior Member

    Tony Athens has done it on the boatdiesel.com site with the 4 cylinder Yanmars. Very good documentation especially in regards to customizing the exhaust systems.
     
  9. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Go looking for a pair of Mercruiser 4.2 diesels with Bravo ll or lll drives. This engine is based on the VM Diesel 706 series; conventional pushrod 6 cyl with turbo and intercooler with computer controlled mechanical injection. A very compact and light package giving 230 to 250 hp with very low consumption and without "space tech". There's even a 300 hp version, but you don't need that to get moving.
     

  10. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    Most of the 28 Bertrams built in Australia were sterndrive either Gas or diesel
     
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