Materials advice, yes i am a newbie

Discussion in 'Fiberglass and Composite Boat Building' started by mberry, Jun 11, 2017.

  1. mberry
    Joined: Jan 2017
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    Location: Australia

    mberry Junior Member

    Hi,

    Ive got a 8.1m cat, built here in Australia. (Markham Dominator)

    As it doesnt look like it will sell im going to punch a bit more money into it and change the few bit about it to make it my perfect boat.

    It currently has a pair of df150s on it which do the job but a bit slow for liking so im going to upgrade with a pair of 225s and extend the transom by another meter to give it more buoyancy in stern to counter the added weight.

    While im at it the deck will get ripped up (theres a few soft spots starting to show) so i will replace that maybe change the fuel tank position and probably replace the stringers too avoid any future problems.

    The cat is a foam sandwich construction, at least the hull is, i am yet to pull it apart and see how much wood is in it. theyve gone out of business so i cant ring them to find out how they were made exactly.

    Anyway my question was relating to the best materials for the job, i dont want to use any wood and like the idea of saving weight using composites but the more i read the more confused to which one is best. one company i have spoken with recommended duflex for the lot including transom, i dont like the idea of a foam sandwiched transom. I was thinking Coosa board.

    should i use coosa board for the transom and use foam sandwich for the deck and stringer?

    Also regards to the extension what layup would you recommend? i know they say its best to match the manufacturer but i havent started the rebuild yet so not sure of their technique.

    I will leave the questions there and look forward to hearing from you, no doubt to be replied with more questions from me. this is a daunting task to take on hence why i am here, i tend to over do things so i would rather be over doing them in the right way.

    thanks in advance!
     

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  2. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    People frequently say they want to use "the best" products, then add up all the costs and start trimming it down to a realistic amount.

    Coosa is foam, the density varies on what you want to do with it, but it does contain glass, so it's strong. You can use Coosa for all of it if you want, including the transom, just different densities as needed.
     
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I would not be in any hurry to do anything, without a thorough evaluation first. Are there inspection ports on the cockpit sole ? That boat looks as if it may have been built to survey specs, it is not, seemingly, a stock build. The registering authority may have a record of what specs it conforms to, but knowing the way these govt agencies operate, you will likely get no help with that. Are there any cracks around the transom(s) or at the junction of the "wet deck" and the inner hull sides ? A spongy floor is not necessarily a harbinger of doom for the rest of the internals either. But you have to know what is under there, and some inspection ports are helpful in that regard. But be careful cutting into that floor, especially anywhere near the fuel tanks, you also don't want to ignite any fuel vapours that might lurk under there, if by some chance there is a fuel leak. If you strike some kind of fastener that can produce a spark, with a saw or grinder etc, with lingering fuel vapours, it could be very unfortunate. I know that some models from that maker had pour foam filling both hulls. Extending that boat a metre is a huge job with unpredictable results, I would be loath to get into that, it seems just not worth it. If you found it hard to sell as an "original", it will be harder still to sell, and recover all your labour and costs, if non-standard.
     
    Last edited: Jun 12, 2017
  4. mberry
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    mberry Junior Member

    Ondarvr, thanks for that response.

    Mr Efficiency, Definitely not in any hurry to go tearing it apart.
    There are two access holes in the aft for the bulge pumps and mid ships to access the fuel tank senders and some forward (i assume there are some inside the cab too but its carpeted and havent ripped it up) ive cracked the ones i can access, there is water ingress into the starboard sponson from the topside (usually after rain), there is survey foam in the forward ones.
    Yes the boat was built to survey (ex nsw maritime), its called a 8.1m but its actually smaller, the 8.1s are rated to 590hp so adding the difference to mine should accommodate the new motors (30" transom). The government agencies are useless, i cant even get the previous certificate of survey from them. Being built to survey basically means they have been built heavier, with bulk heads pass a stability test and have positive buoyancy, which is partly the reason i want to rip up the floor. I know they removed some of the old pour in foam and replaced it with newer non water absorbing stuff (cant remember the technical name) which what the front hatches have. i want to remove any that may be left behind.
    I wont be selling the boat after the work is completed, ill be doing a few mods to make it my ideal boat. ive had several now and this thing only needs a few 'tweaks'. I enjoy a challenge, this will be one hell of one and i wont be going at it half arsed. would definitely make it easier if they (markham) didnt go out of business!
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    It was a 24 footer, that boat, I think, not sure what the reputation of that particular hull was, some of the smaller ones were nothing to get excited about. It seems not to be rated as comparable to Shark Cat/ Noosa Cat or Kevlacat in that size range. It has the rounded hulls, which are a mixed blessing at best. Removal/replacement of the floor panelling is not a big job of itself, but structural work beyond that is, and, like marriage, not to be entered into lightly !
     
  6. mberry
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    mberry Junior Member

    Yeah thats the one. Apparently not as well perceived as the shark/noosa cats, just have to look at the forums and they get a bashing but as pointed out its how theyre driven. mine has been great, the only major flaw is that the cab is built like an out house and rolls a bit at rest in sloppy crap, as you mentioned the rounded aft hulls probably dont help. Under way its hard to fault, weve got a house on wedge island here in SA and regularly run out there (30 odd k offshore) and come home in some crap stuff, not talking 35knots and 8m swell like some people believe they do. but genuine 3m and 18knots of slop and ive never felt un easy. Id love a noosa cat but the budget wont extend that far, having said that ill do anything to get out of sanding fibreglass haha.
    Re the floor and structural work, no doubt it will be a big job. if im going to the effort of doing the floor im going to bite the bullet and do the complete boat, the paint is daggy too, windows need a reseal and another paint too, all those little bits that just ad up. As mentioned previously i get carried away so i couldnt just replace the floor as id see something else to do and so on, so i am better off stripping the boat and rebuilding it in entirety the way i want it in a way that will last for hopefully another 20plus years to how i want it.
    Might see if i can trade it in on a noosa cat haha
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I seriously doubt you'd get any noticeable speed gain out of bigger motors, even if you extend the hull, which is a daunting task. Those round bellied hulls don't get out of the water like chined boats.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Wow, just looked at some pix of that 24' hull, the tunnel is very narrow aft, there should be ample lift, rounded or not. Quite different to the smaller boats of that brand. I reckon I'd follow the Beatle's advice and "let it be", barring replacing obvious rot and corruption. I saw one that sold recently in SE Qld with twin podded V6 2S Mariner o/b. I never noticed the slimness of that tunnel aft, possibly because it was black anti-fouled. Went for low-mid $20k's.
     
  9. mberry
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    mberry Junior Member

    the hulls are narrow aft, the hulls also (bit hard to explain) screw towards the stern aswell giving them more lift. due to the weight of it i think it would benefit from larger motors, the little 150s work for their money. the reccy versions are still up around 70-90k (tidier than mine but less whistles) but noone has any money these days and the ex commercial and decent hours dont help a sale.
    As you mentioned i may just address the rot and leave it, im 300ks away from it so its hard to address what i really need to do.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Looking underneath boats of that make is rather giddying, what with the twists and turns and convolutions, the nett effect of which was (supposedly), amongst other things, to have the turning behaviour of the boat an improvement on other more conventional catamarans. That always seemed a "problem" not worth "fixing". In fact the aircraft-carrier like turning circle of the old cats went hand-in-hand with their broach free handling.
     
  11. mberry
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    mberry Junior Member

    it definitely has some benefits over the conventional cat hulls, its extremely dry, all the water gets funneled down the hull and very little goes sideways unlike the others. it does get a bit of spray back through the tunnels if it comes down stern first but not unlike all other cats.
    i havent had any close to broaching situations (touch wood) but i do drive with reserve, i think some of the bad news about these hulls probably come down to the driver. they are very trim sensitive. i would be keen to know how many of the new owners had skippered cats prior. I hear you with turning circle, not really an issue, just slow down, drop the revs on the inside motor and away you go. id prefer my hulls to be conventional but its not the case and its alot of boat for what i paid for it so if it comes down to it i dont mind throwing some more money at it.....after all it is a boat thats what theyre best at haha
     

  12. Mr Efficiency
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    Mr Efficiency Senior Member

    If you are happy with the handling as is, it is inadvisable to be doing extensions, I would say.
     
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