How to increase buoyancy?

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ddakota

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Jul 11, 2009
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OK - for the pros out here -I have searched the forums and cant find any threads on this issue, so if there is already one here, please advise. If not, I have a new puzzle for you -

I have a 19' Bayliner Center Console that is in good shape. The 125 Force that came on it finally cratered and we put a Johnson 175 on it (it was free) and it runs like a bat outa h.... Slight problem though - the motor is a little too heavy for the boat. The boat sits about 3"-4" deeper in the water at the transom now with the increased weight of the 175. The self bailing drain holes in the splash well are right at water level now. SO now, water will flow back into the splash well. I can keep it in the splash well by plugging the drain hole in the splash guard so it does not run up into the boat.

For a lot of reasons, I would like to have the boat sit higher in the water. For that I need to increase the buoyancy factor of the boat and I cannot figure out how to do that without adding something to the back of the boat. Something in the way of small pontoons (like trim tabs - maybe boxes filled with foam) or a motor mount extension for the transom - one of those thousand dollar swim platform extensions people advertise.

My dad said just pour some flotation foam in the back of the boat. I tried to explain buoyancy does not work that way, but he is hardheaded. Or am I wrong ( I think I remember my physics correctly)?

The advantage of going the motor mount extension route is I could also install a hydraulic jack plate on it and run the shallow Texas flats I fish better. I can do that anyway to the transom, but if I need to stick something on the back of the transom to solve this, might as well add the jack plate to the back end of that also.

any ideas???? I really don't want to spend a couple thousand bucks on this little problem, so any suggestions would be welcome.
 

NoKlu

Senior Chief Petty Officer
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Feb 23, 2008
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Re: How to increase buoyancy?

Putting or moving some weight [battery and fuel] up to the front might raise the back end enough.
 

Bondo

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70,585
Re: How to increase buoyancy?

Ayuh,... Buoyancy can only be increased by displacing more water....

I suggest a Bigger boat to match the Oversized motor...
 

rosser1

Petty Officer 1st Class
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Apr 5, 2009
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Re: How to increase buoyancy?

yep cover more area with boat, wont work or put more weight up front. i did. put trolling battery and extra fuel tank under front seat of bass boat.
 

5150abf

Vice Admiral
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Re: How to increase buoyancy?

As stated, there are 2 ways to make a boat float better, get rid of weight or make the hull bigger.

The back of the boat already weights too much, if you put a 100 lb jack plate on it too it will only make the problem worse.

And the big one, is the boat rated for an engine that big?

If not then you really don't need to worry about it since the engine will at some point rip the transom out of the boat, then you won't have a boat or motor, problem solved.

Seriously, over powering a boat is VERY dangerous, when they fail it is suddenly and normally at speed so by the time you realize there is a problem you are sinking.

But no, other than adding displacement to the hull it wil not float better.
 

ondarvr

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Re: How to increase buoyancy?

You didn't say what year bayliner it is, but since it had a Force on it I'll assume it was an older model. Check the transom, deck and stringers for rotten wood, plus you may have waterlogged foam, this will make it sit lower and hurt performance.
 

ddakota

Seaman Apprentice
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Re: How to increase buoyancy?

I think the boat is an 89 model - yes its old, but everything is still in good shape. The boat is overpowered now. I think it might be rated for 125 - 135 HP at most, so the 175 is too much motor for it. There are no visual signs of transom failure, but as you stated - when it fails, it will probably be catastrophic. I should consider a transom replacement if I want to continue to use this setup....or as the boat dealer told me - a new boat. I told him that seemed like a good idea, then asked did he have an idea where I might find one, since he brought it up.....wouldn't you know it, he just happened to have a parking lot full of them....imagine that! I guess a few grand is still cheaper than the new one, but I was taught old math (2+2=4 and being close does not count - you still fail) so I am not sure I am calculating correctly.

thanks for the comments. I will stay in the flats of South Texas so when I sink, I can walk back.
 

pinecrestwoods

Petty Officer 2nd Class
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Jun 17, 2009
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Re: How to increase buoyancy?

Maybe I read wrong, but there was mention of moving battery, etc. to the front. I don't think they meant to add weight to the front and leave all of the weight in the back. I think they meant to transfer the mobile items to the front. I don't know what the weight difference that 50hp made.

Talk to your boat dealer friend and see if you can work a trade for the 175. Yes, it's fun, but it's already giving you headaches, and it sounds like it will only get worse. Place some ads?...... just make sure to thoroughly check compression, etc. or everything that may come down the pike.
 

henrye718

Petty Officer 1st Class
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May 24, 2009
Messages
207
Re: How to increase buoyancy?

I guess move the gas tank and the batts up front and do not run that motor wide open ever is your only hope.
 

miguelsanta

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Apr 25, 2011
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Re: How to increase buoyancy?

Hi
I have a prolne 1991 walk 21 foot with yamaha 150hp outboard same year
transom looks in good conditions but i have noticed that the transom flotation line after years is more deeper or more close to the water reaching almost the drain area. this happens with with 7 adult on it. in the past I did not noticed that.
I worry about that.
I was thinking to add some foam in back because at both side of the boat it does have some emphy spaces under the batteries and the other side under the seat.
Will this increase the bouyancy on the transom area?
 

Deuce76063

Recruit
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Aug 3, 2009
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Re: How to increase buoyancy?

You can fill the hull of your boat level full of foam, and it won't float any higher. In fact, it will sit lower due to the added weight of the foam. The only way added foam will make your boat float higher is to find a way to put the foam on the outside of the boat, and then encase that in a larger hull. Easier to just buy a larger boat, I'm thinking.
 

Art Bernard

Banned
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May 4, 2011
Messages
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Re: How to increase buoyancy?

If the 175 was a freebie, sell it and buy you a good used motor that will fit the boat, problem solved.

Art
 

Woodonglass

Supreme Mariner
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Dec 29, 2009
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Re: How to increase buoyancy?

If your boat is sitting Lower in the water than usual You might want to check for waterlogged foam below the sole(Deck) of your boat. This is a very common issue with boats. It is very easy for water logged foam to add up to 1,000 lbs of additional weight to a boat. I would Highly recommend that you investigate this possibility. You could contact the manufacturer to see if they could provide you with the estimated weight of the boat when it was built and then weight it to see what it weighs now. If there is a significant difference then You may have found the problem.
 

petermarcus

Petty Officer 2nd Class
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Apr 30, 2010
Messages
129
Re: How to increase buoyancy?

Probably should have started a new thread, Miguel. This thread originated 2 years ago.

I do agree with WOG, though -- if your boat was higher before and lower now, you're probably looking at something making it heavier. Odds are, that's water, either rotting the wood or soaking into the foam.
 
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