Buoyancy Issue on 2670 Glacier Bay

Discussion in 'Boat Design' started by finmanfish, Nov 5, 2013.

  1. finmanfish
    Joined: Nov 2013
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    finmanfish Junior Member

    Hello everyone I am new here and my name is Vince. I own a 2670 Glacier Bay power catamaran fishing boat. I am looking for an elegant way to add maybe 500 lbs of buoyancy to the stern. When we are loaded down for a fishing trip we are submerging the motor wells at rest. Here is a link with photos of the boat. Open to any creative solution. Thanks and look forward to your opinions.

    https://www.google.com/search?q=gla...tHfSwsATDlYCwCw&ved=0CCoQsAQ&biw=1024&bih=667
     
  2. rasorinc
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    rasorinc Senior Member

    Do you have any opening bays in the floor or sidewalls near the transom where you could put rigid stryofoam in?
     
  3. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Adding foam internally near the transom will have almost zero effect on "When we are loaded down for a fishing trip we are submerging the motor wells at rest. Here is a link with photos of the boat." Almost zero effect because the weight added by the foam will push the stern down further.

    What is needed to keep the motor wells from submerging is added volume near the stern. 500 pounds is 7.8 cubic feet in salt water or 3.9 cubic feet per side. I've heard of hulls being extended aft but have no idea if that is feasible on the OP's boat.
     
  4. Stumble
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    Stumble Senior Member

    It really isn't feasible to add hull extensions. The motors are mounted on the transom, so there is no where to add them.

    My first thought is you may be overloading the boat from the get go. How much gear and how many people are you putting aboard?

    Secondly, are you just submerging the transom or the whole boat? If just the transom then you may need to move some of the weight forward to balance the boat out.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, you have water sloshing around in the motor wells at rest. That in itself is not a real concern, unless there is a problem with the powerheads being too close to the water, which can be an issue with cats, because the draft is generally greater with the smaller waterline plane area compared to a monohull. However, longer legs on outboards has helped this issue, I had a cat that was built like a brick outhouse, overweight, and water sloshed around in the wells, but the XL shaft engines never drowned. Had they been 20" shaft they almost certainly would have sooner or later, though. I don't see any real prospect of adding 500 lbs of bouyancy aft that is not going to drastically affect the dynamics of the thing underway. What might work better, as Stumble has suggested, is to re-locate some of your extra loading well forward in the boat, that should lift the stern nicely.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Yep, trim is the issue, not floatation. Trim the boat properly and the problem goes away. The first thing you have to ask is how much of this stuff just has to live in the cockpit and how much can go below. A 100 pound weight 5' forward of the CB will balance you out.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Move weight forward and it will go better up and running as well. Power cats with too much weight, too far rearward, are unhappy boats.
     
  8. PAR
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    PAR Yacht Designer/Builder

    The reverse is true as well, though she'll like the forward bias better than aft as mentioned. Empty the boat, place gear to trim properly and she'll be happier for it.
     
  9. finmanfish
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    finmanfish Junior Member

    thanks for the input gentleman. I should tell you all that the problem is fuel load. This boat carries 260 gallons of fuel and the heavy stern happens when we have a full load of fuel. The boat came with 18o gal, 90 on each side then we added 40 extra per side and that caused the problem. we put is as far forward as possible but it wasn't far enough. It would not be easy to arbitrarily but equipment forward to balance it but perhaps a deliberate attempt at counter weighting the bow would be the ticket.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Counter-weighting with dead weight is not really a sound solution, can you fit a couple of fuel bladders above floor level well forward, and not use the 40 a side ones ?
     
  11. Stumble
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    Stumble Senior Member

    Fin,

    My guess is that you have that boat loaded way past its load limit. I couldn't find the numbers for the 2670, but let's assume its 1,200lbs.

    By the time you account for the added 480lbs of fuel, plus say 40 lbs for the two new fuel tanks, four people at 180lbs, 100lbs of ice, and 50lbs of fishing tackle, 20lbs of drinks and food, ect... you are sitting at a total load of 1620lbs. I haven't even started a real weight budget, but frankly I think you are grossly overloaded. There isn't a solution to this except removing some weight, either by running with the two tanks empty, leaving people behind, or just going out slower and putting people in the bow until you have used the fuel up.
     
  12. Ike
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    Ike Senior Member

    I think Stumble has stumbled on the real issue. First you added 40 gallons of fuel which is an additional 240 lb. Then you pack all that other stuff aboard and you far exceed the load capacity of the boat. 260 gallons of fuel is a grand total of 1560 lbs. She was designed for 1300. Adding weight to counterbalance the weight aft would just compound the problem. You need to decide what you can do without, and get rid of 200-300 lbs as far aft as possible to bring the stern up.

    Oh yeah, get rid of weight and you will get better fuel economy and it will go farther on less fuel.
     
  13. finmanfish
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    finmanfish Junior Member

    No it isn't overloaded. I checked with the factory when I did it. It can do 2200 lbs. I want to add some type of permanent buoyancy in the rear.
     
  14. tom28571
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    tom28571 Senior Member

    Without changes to the basic hullform aft, that is not possible.
     

  15. messabout
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    messabout Senior Member

    Never mind what the factory told you. Surely you don't think the factory would shade the truth :(

    The problem is excess weight and improper placement as others have advised. Cats are not particularly burdensome, in fact they are quite sensitive about weight and weight placement.
     
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