change deadrise

Discussion in 'Boat Design' started by ezyl74, May 23, 2009.

  1. ezyl74
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    ezyl74 Junior Member

    Hi all I am rebuilding an aluminum Marrinette, 32'x12'. I plan to change the deadrise as the hull in it's stock form is all but flat at the stern. Also in the plans are to lengthen the hull by about 4' and get rid of the inboards and install new outboards. And finally build a new cabin. I have the hull and the ambition and the skill what I lack is the design knowledge. I would like to get the boat drawn up in it's stock form and then draw it in it's new shape and run stability tests to compair. Who can do this for me or could I get some software and struggle through it? Any thoughts?
     
  2. lewisboats
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    lewisboats Obsessed Member

    You are looking at MAJOR changes. You should consult a Naval architect to do this...it isnt something that can be done by someone without engineering and design knowledge

    Steve
     
  3. ezyl74
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    ezyl74 Junior Member

    That is why I am trying to get some help. I am in contact with a guy who can draw it up(autocad) but can not do any stability testing.
     
  4. marshmat
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    marshmat Senior Member

    Hi Ezyl74,

    If I read correctly, the situation is as follows:

    You have a 32'x12' aluminum boat, inboard powered, with a nearly flat bottom.

    You want a 36'x12' aluminum boat, outboard powered, V-hull, with a cabin.

    What you're talking about isn't so much refitting or modifying an existing boat, as cutting an existing boat up for scrap to use in the building of a new boat. Refitting an existing hull is one thing, but when you start talking about lengthening the boat by 13%, changing the hull shape, removing 1200-1600 pounds of engine from amidships and adding 1000 lb of engine two feet back from the transom.... you're really talking about building a whole new boat, and frankly, that would be a safer and more economically viable option than hiring a team of engineers and welding experts to try to drastically reconfigure an existing hull into something that may or may not work, but will almost surely have lowered residual value.

    If you think you can live with the hull you have, maybe refitting it is the way to go. If you're not happy with the hull, to the extent that you want to lengthen and reshape it, you're probably better off to look for a more suitable used hull or build a new boat.
     
  5. ezyl74
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    ezyl74 Junior Member

    I have thought of finding a different hull but in the 2 years I have been looking have not come up with anything more cost effective or better. I may show some ignorance here, but people have been building boats without modern tools for many many years. They worked. I have seen 2 other Marrinettes with simmilar things done with no ill effects. I realize this is no small project, and I want to consult a pro designer. But who?
     
  6. dobsong
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    dobsong Junior Member

    You hav e to wonder............

    Yes I agree but rhen again there are some people who have more $$$$$s than cents
     
  7. ezyl74
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    ezyl74 Junior Member

    I thought that I may get some insight by people in the industry and instead I get critics and synics. I have aquired more usable info from the fishermen in the local tavern. Very disapointed. You obvesaly underestimate me. The sad part is you do not even know me or qualifications! At what point does your vast knowledge go to waist if you are not willing to share it.
     
  8. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Ezyl,

    You are correct, we don't know you or your qualifications. And yes, there has been some critical and, yes, even cynical response to your proposal. This kind of reaction is, in fact, fairly routine on web forums of all sorts, whenever a new member comes along with a radical, complex plan. It's not unique to bd.net.

    I'm not a naval architect- I'm an engineering physicist. And I don't personally know any NA who does this kind of refit work. What I can offer, based on my (admittedly limited) understanding of naval architecture, is this:

    - A 13% increase in length leads to a corresponding increase in displacement and structural loads. Unless the boat was grossly overbuilt to start with, this could mean reinforcing the existing frames, beefing up longitudinals, adding all sorts of extra bracing here and there... what seems like a small thing could lead to a lot of extra work.

    - Converting a flat to a V bottom hull could mean either cutting out the entire bottom of the hull and rebuilding it (complete with new internal structure), or it could mean effectively building another hull bottom (again, complete with internal structure) onto the bottom of the existing hull.

    - Converting from inboards (you did pluralize it, so at least two engines) to outboards means removing a thousand pounds or more from the middle of the boat, and adding a thousand or so to the transom. It's like taking a balanced teeter-totter with a couple of kids on each end, and moving one of the kids to the other side. Without extremely careful attention to the centre of gravity and the overall weight distribution, this can result in a boat so badly balanced as to be unusable.

    - Major structural reconfiguration can drastically affect the resale value of a boat, and will certainly raise lots of surveyors' eyebrows if you ever try to sell it or have an insurance inspection.

    It's possible- but not necessarily a good idea. The structure of most metal boats is carefully designed for the anticipated loads of that particular boat, based on long, very tedious engineering manuals- very much unlike traditional wooden construction, where everything was just built as insanely strong as necessary to make the builder comfortable with his product.

    Stability-wise, the calculations for such a revision are not terribly complex. Structure-wise, it could be a nightmare.
     
  9. ezyl74
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    ezyl74 Junior Member

    You are obliviosly an intelegent and quite articulate. This plan is somewhat thoughtout. The weight distribution issue created by moving to aft mounted outboards is going to be negated hopefully by the new raised pilot cabin arangement that is mounted far forward in the hull. Substantial modification to the stringers and a heavy keel will be added to bolster the hull structure. Hopefull the added weight of the new cabin and interior parts will offset the added flotation of the increased deadrise and length. These are the details that need to be fine tuned. Marrinette yachts in the early 80s made a change to the deadrise, they called it a canoe hull. They welded a large canoe shape thing to the bottom of the hull that changed the deadrise. Other than the canoe the hull is nearly the same. The big ? why do this. Because I WANT the challenge. The hull was near free. I have about 70 grand to get this done. I have priced many boats both new and used and none fit the application and all are far more than money than I have. If anyone knows a builder that will build a boat this size within the budget I have please come forward. I guess what I wanted out of this forum was to try to get some leads of people who would want to draw this project for me, or find out more about the software to draw it myself. No spellcheck sorry
     
  10. TollyWally
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    TollyWally Senior Member

    My area of expertise is much closer to the fisherman in the tavern than a naval architect. That being said I've seen some radical changes made to boats. Some worked, some disappeared with all hands.

    The way I see it you've got 70 grand budgeted for a 36 ft tin boat. Does that include the price of the motors? Do the old inboard systems work?

    Talk to me a little bit and I'll give you the benefits of my insight. But rest assured, none of these guys are giving you bad advice. You're proposing a complicated project that can go wrong easier than it can go right.

    You mentioned that there were several similar boats that had undergone conversions more or less successfully. Talk to those guys, take lots of pictures, ask lots of questions.

    Lastly in this economy 70 grand cash makes you someone that boat sellers desperately want to meet. Just a suggestion'
     
  11. ezyl74
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    ezyl74 Junior Member

    I guess the way that I see it I am not doing anything new or radical. I am building a deep V very similar to thousands of other deep Vs. I have seen deep Vs in all power configurations and sizes. I am sure some hulls were more sucessfull than others. I am not crossing oceans but am well awair what can and does happen everyday. I have talked to 2 guys who have added length to the same boat I am working on and there attude was very casual. Very easy to do one said. The 70k includes motors to the tune of about 30k. I am no strainger to looking for good used parts, those of which are probably better than could be bought new. Labor is supplied by me (free). I have made offers on 3 boats that would have all need work to make them usable. I am looking at a 40 footer now but needs a lot of cabin work and new power. $$$ I want and like aluminum so finding something not beat to hell by a fisherman or an old crewboat is tuff. Striker built some very good aluminum boats but they are all sport fishers and the cabin is not conducive. The boat I have now is a clean slate and a good start, they were well built and have a strong following. your thoughts are welcome
     
  12. TollyWally
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    TollyWally Senior Member

    So I went to this site http://www.marinette.com/te and found a 32' express cruiser at 32 x 12. Is that similar to what you've got?
     
  13. ezyl74
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    ezyl74 Junior Member

    Yes it is similar. Hull is same but cabin is different. They made 3 or 4 models based on this hull.
     
  14. TollyWally
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    TollyWally Senior Member

    So I think stability tests and drawings are a great idea. If you can get some factory lines it would make your job a lot easier. Is the cabin really that trashed or are you thinking of moving it for balance issues?

    I wonder how many systems you have to disrupt to get the kind of access etc. you need to pull this off. Commercial fishing boats are grafted onto all the time. But it sure can be an awful lot of work. If you can get the hull for very cheap, am I correct is assuming the boat is pretty well worn out at this moment?

    I think you can probably pull it off but I don't think you'll save much money but who knows. What ever you do, it make for an interesting story and lesson for others regardless of the outcome. Good luck.

    I'd consider joining the metal boat society. Look them up and kick in the meager amount of money to join. LOL, which I was too cheap to do but still should. :)
     

  15. ezyl74
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    ezyl74 Junior Member

    I have looked at the metal boat society. Not much factory info is available. I am in contact with the curent owner of Marrinette Yachts, as a matter of fact that is where the hull is coming from. The hull is in very good condition. Like almost all Marrinettes it was a pleasure carft and not worked hard. Every system will get changed ie electrical, plumbing, tanks, ect. Stability test would be great but hard to get somebody to put there name on it. Thanks
     
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