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Thread: Heavy Back end!!!

  1. #106

    Re: Heavy Back end!!!

    There is a fair amount of volatile materials when using resins and I agree working on memory of 5 years ago (where did that come from) is not optimal but once again, how was it identified that there is no water in the hull?

  2. #107

    Re: Heavy Back end!!!

    Quote Originally Posted by gazza2006au View Post
    I think the full story is not t
    With us, the transom was rebuilt 5 years ago so technically we are compairing a 5+ year old memory of how she rode to todays ride

    Either that engine was not on there 5+ years ago or someones nemory is vague kind of like your first love

    I read chopped mat 1x1m will will soak 1.5 times its weight

    My recent transom took around 14-15 litres using chopped mat and cloth

    This just isnt working out we are missing the key here
    Gee Gazza my transom is epoxy twin twill 680gram carbon with 450biaxial over that and I think theres only 4.5 liters to do that for a 6foot transom.

  3. #108

    Re: Heavy Back end!!!

    Hey Chris my first transom used 24 litres that was outside skin 1 layer of 900gram double bias than 9 layers of 400gram double bias, inside skin was 2 layers 400gram double bias plus 4 layers of tabbing

    The new transom has 3 layers of 450gram chopped mat, 3 layers of 400gram double bias, kept the inside skin and tabbing but i did use a ton of glue to glue my core material in some oozed out, this transom used about 14-15L epoxy

  4. #109

    Re: Heavy Back end!!!

    Hey Digs a little birdy whispered in my ear about the 5 years, when the thread was started i assumed it was a new transom/freshly done and the boat was used recently before the transom repair

    A lot of memory can fade over a long 5 years

  5. #110

    Re: Heavy Back end!!!

    Again guys, I appreciate everyone's feedback. Digs, there is nothing wrong with my memory, it has only taken me 5 yrs to put a post on here to get any ideas on how to correct my issue. (was hoping for a quick and simple and cheap fix). the maiden trip after the new transom I was in shock on how low the boat sat. obviously i went back to the transom installer to work out what happened and how to correct it. there was not a fix from him. so i have put up with this for 5 years before I have posted. I have drilled holes where gazza asked me to and is bone dry. I replaced the donk 12yrs ago from a 70 Evinrude to a 75 merc 2 stroke. slightly heavier motor but made no impact on the arse end until I had the transom done. I have put 80 litres of water bottles at the bow for 1 trip but didnt seem to work either.
    Digs if you are local to Northside of Brissy, i could always bring my boat over and show you.

  6. #111

    Re: Heavy Back end!!!

    Sunshine Coast mate but do spend a lot of time in Redcliffe if you're anywhere near there.

  7. #112

    Re: Heavy Back end!!!

    Nealeboy can you tell by looking at the splashwell if he drilled the motor holes in the same position and are you sure the motor is mounted at the old height?

  8. #113

    Re: Heavy Back end!!!

    Hi Fed, yes ive gone all over that and believe the mounts are the same.

    Dignity, i will PM you with my Mobile and when you have spare time next at Redcliffe we can chat as im not far from there.

  9. #114

    Re: Heavy Back end!!!

    i got the transom, floor and stringers replaced

    Its not just the transom that was worked on. It was the floor and stringers as well.

    THAT'S why its heavier and that's why moving the existing "furniture" around has no effect.

    The boat needs more flotation at the stern.

    Best suggestion now is to go and look at flotation pods to provide that.

    U may see value in experimenting a bit yourself first maybe by strapping an airtight container on either side of the o/b leg (while the boat is on the trailer or maybe raising the motor high enough to strap 1 on each side then lower it into the water so that the airtight containers are then under the water.

    Maybe a couple of empty 3L milk containers. Convenient handle for fixing to prop or something. Enough flotation from them to tell if u're thinking in the right direction. Cheap, effective and easy to do by self

    U can change the volume of the air inside the container by lifting leg , take lids off and adding water. That'll change the amount of flotation and you'll easily see if adding flotation at the stern is the answer (does the boat sit lower or higher as you fiddle with the containers).

    Mucking around with tests like that will indicate what needs to be done plus u'll have the satisfaction of "nutting it out yourself" (if it works).

    If extra flotation via pods IS the answer, then go and see somebody who installs them to get advice on how big they should be.

    If that's the solution, then the amount of flotation required is equal to the volume of air left in each container after u add sufficient water to each to get the "sit" in the water that you want. (Adding water to a container reduces the volume of air that's available to provide buoyancy).

  10. #115

    Re: Heavy Back end!!!

    I think the picture is a bit of an illusion, I measured the stationary attitude at less than 2 degrees.
    https://www.ginifab.com/feeds/angle_measurement/

  11. #116

    Re: Heavy Back end!!!

    Assume that your 2 degrees is correct, Fed

    That means (from simple trigonometry) that the front of the boat is 7 inches higher out of the water than the stern because 2 degrees over 16 ft = 7 inches.

    Trigonometery calculation: Tan = opposite/adjacent...........Tan 2 (degrees) = Ht (extra bow height out of water from level) / 16 Ft (length of boat)..........0349 = Ht / 16ft............= HT = .0349 x 192 inches ....... = 7 inches.

    Therefore stern is sitting down 7 inches lower than the bow. The stern is sitting 3.5 inches lower in water and the bow is sitting 3.5 inches higher than it was (IF the boat was level previously).

    However my protractor says 4 degrees which makes the stern 13 inches lower than the bow to be level.

    That's not as bad as it first sounds though.

    In your case of 2 degrees, the bow only has to come down 3.5 inches and the stern up 3.5 inches to be level (simplistically thinking).

    In my case of 4 degrees, the bow needs to come down 6.5 inches and the stern up 6.5 inches to be level.

    Remember that the balance point in the water is the centre of flotation and NOT the centre of gravity.

    To me that means that 3 inches of flotation at the stern ( thereby moving the centre of flotation towards the stern) might very well translate to bringing the bow down 6 inches or so because of the differing volumes involved.

    Bit of fiddling still involved.

  12. #117

    Re: Heavy Back end!!!

    Late to this thread but I'm going to go against the grain and say there's nothing wrong with how it's sitting - that's typical attitude for pretty much any 16' half cabin. Check out the pics below that show yours vs a couple of other V16Cs, all with very similar attitude at rest or idling along. Critical points of comparison - the chines are just underwater at the transom, and the chine / forefoot / stem junction (whatever that point is called!) occurs about halfway between the waterline and the end of the bow.

    The paintjob on yours makes it look more bow-up, stern-heavy than it is as the solid green emphasises the rising gunwales instead of the deck / hull joint like the white-with-red-band vessel.

    The exhaust relief hole being submerged isn't unusual with a 20" leg if you have the outboard trimmed full-in at idle. Some Mercury owner's manuals actually cover that and tell you to just trim out until powering up per the attached extract. I agree with others that your outboard is a bit low though and could do with being 1 hole higher (probably ~3/4" or 20mm).

    Given the described scenario of (1) water splashing into the exhaust relief port; (2) anti-ventilation plate being below keel per your photo; (3) prop ventilation occurring if you lift the motor higher and (4) excessive bow-up attitude when getting onto the plane, I reckon this is one of the few times that I'd say installing a hydrofoil might help more than it hinders.

    I'd lift the motor one hole so that the anti-ventilation plate is inline with the keel when trimmed at 90°, fit a hydrofoil (one of the longer-than-wide style; not the wide whale-tail variety) to suppress ventilation and see how that goes. You're on the lower end of the power range with a 75hp on that hull so the foil should also help lift the stern and improve behaviour lifting onto plane.

    Water into the splash well from waves approaching from the stern is the norm with 20" transoms. It's the reason that you have a splash well instead of just an open transom.

    0f33gFH.jpg6Z0OUM4.jpgpAEI8yQ.jpgzxAspAI.jpgf6gSm4s.jpg

  13. #118

    Re: Heavy Back end!!!

    This has been niggling at me and I found the following diagram in 'Inboard Motor Installations' by Glen L. Witt (of Glen-L Boats) and Ken Hankinson dealing with hull balance. It shows the keel level and parallel with the water surface when the hull is in balance.

    nEfA35K.jpg

    What this means is that it should be pretty easy to check and correct overall trim (the combination of weight, buoyancy and load distribution) using the following procedure:


    1. With the boat on the trailer and a digital spirit level on the keel, adjust the jockey wheel until the keel is horizontal (0° on the level).
    2. Choose a reference point on the gunwale, place the level on it aligned fore-aft and measure the gunwale's angle relative to horizontal at that point. Record this measurement and note the position of the level so you can repeat it later on the water.
    3. Float the boat in calm water with a normal loadout. Measure the gunwale angle at the same location and adjust as follows:
      a) If the gunwale angle is less than it was on the trailer, you're trimmed bow down. Adjust weight aft.
      b) If the gunwale angle is greater than it was on the trailer, you're trimmed bow up. Adjust weight forward.
      c) If the gunwale angle is the same as it was on the trailer, you're trimmed correctly. Your keel is parallel with the water surface.
    4. Standing on the boat centreline, measure the dash or transom angle across the boat. If it's not 0° then you're listing to one side. Adjust weight to port or starboard until the list is gone.


    Once you've done that, your boat will be trimmed correctly at rest with keel parallel to the water surface and no list. For that particular loadout anyway - obviously fuel use and people moving about will affect trim during use, but it's a good starting point nonetheless.

    Working out whether you're too heavy overall is a different matter. From what I've read, if you have a hard-chined boat correctly trimmed then the chine should be just below water level at the stern with the wetted chine length extending only "a small percentage" (no value specified) of the hull waterline length.

    You can check that by taking a zoomed-in photo from some distance (to reduce parallax error)
    like OP did and measuring wetted chine length (LC) + waterline length (LW) on the photo, then calculating LC / LW * 100 to give the wetted chine length as a percentage of waterline length.

    0f33gFH.jpg

    It's my guess that if your boat is trimmed correctly and wetted chine length is significantly greater than 5%, you're probably running a bit overweight. I suspect many small boats do as weight adds up quickly.

  14. #119

    Re: Heavy Back end!!!

    Nealeboy

    Look closely at the diagram from Glen_L boats. Magnify the small print under the diagram.

    It describes what the diagram is attempting to show.

    That is: what happens when the relationship between the Centre of Buoyancy (CB) and the Centre of Gravity (CG) changes. The boat will sit "bum down" or "bum up" to a greater degree than what it did BEFORE

    the changes were made. THAT'S what was spoken about earlier (post 116).

    Its a very simple matter to test that by fiddling with those empty airtight containers that I mentioned previously.

    I think that this thread has been approaching your problem from the wrong end. Its been concentrating on possible reasons for what's happened (and look for a solution there). Those suggested reasons have varied greatly and (though well intentioned)

    have simply confused the issue.

    What you are looking for is a solution to the problem rather than a reason for the problem.

    Once you find a "fix" by experimentation, the reason becomes irrelevant. Only the fix is relevant to you.

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