bouyancy test

hi all
I am sure that you might be able to help understand the weight of my boat.
I bought a 2009, 15 foot well known boat without a bouyancy certificate, but due to the model did not think that it would be a problem,
I weighed the boat today and the weight was 1120 Kg.
Subtract the trailer 220Kg and motors+batteries 200Kg and boat spec weight of 350Kg,that is 350Kg over weight. The manufacture claims that it is filled with closed cell foam but somewhere in the hull there is 350 liters of water.
Is this assumption correct?
The scale was at the dept. of traffic, so calibration is correct. I drilled a small hole in the side of the fish hatch to check for water but nothing was found.
It seems that the only option is to open the deck up and check. Can closed cell foam absorb and retain water?
Are foam filled bottles not a better system that could allow the water to drain out?
Your comments and input will be appreciated
thanks

Foam certainly does get waterlogged. I know that I'm going to get shouted down by some but in my most humble opinion, bottles are a much better solution. The correct hexagonal bottles should be used.

I have a boat that I'll be doing up sometime this winter. When I do it, I will glue each bottle in place with a dab of PU adhesive and glue each subsequent bottle to one another as you build up the depth of more bottles. What you need to avoid is the bottles all spilling out in the unfortunate event of a hull breakup at sea. Some guys put bottles in a retaining net but perhaps the best would be a combination of the net and the PU glue.

After all the bottles are in place, I'll put in foam to fill the void between the bottles and the deck.

The first thing I learned in boat building was to never have any place where water can accumulate without being able to easily drain. Foam, to my mind, is just one such situation. I only understood this about foam when I had to cut some out to get to the lower engine bolts. The foam was wet and heavier than it should have been.

your tread is in a sense, incomplete!
what extras do you have fitted?
a boat of 350 kg is very light, so, please tell us, what boat you have.

the bad thing in my view, with regards to bottles:

in the old days, they used 1 litre milk bottles.
on the wit blits, I had, the bottles rattled inside the hull, with this, the aluminium heads wore through and water entered the bottles. so even if you did remove the bungs, not all water came out as many of the bottles were filled with some water.

the other aspect, when you live up here gauteng, where do you decide to do buoyancy?
placing a milk bottle in a hull, up here in Gauteng, where air pressure is less!

so by the time you get down to the coast, the milk bottles have shrunk a bit!!!

or do you do it down there, and when you come up to the reef, the milk bottle will expand, again due to difference in atmospheric pressure!

closed cell or foam is much better to a certain degree.
before foam filling your hull, the whole hull needs to be sealed "coat or two of fibreglass", then you fill the foam.
then you seal the deck, and make sure it is completely sealed!
also mixing a 2 part foam in different heat situations "winter and summer" will also have a different outcome!

but then again, they want inspection hatches in the vessel, so make sure, they are placed where soaking in water is not present as they tend to leak.

using sondor foam, seems to be the best option.
it is the most expensive foam "closed cell" and is like a mattress, ie can be formed to fit the cavity of the hull.

with sondor foam, bungs is advised as the hull will drain.

with each of the buoyancy aspects, some have their positives and some more negatives!

so let hear more about your situation!!

the boat was weighed empty with only the motors, controls and batteries, thus 100 Kg per motor.(Spec 75)
the hull weight was obtained from the dealers website and is stated as 350 kg.
I spent most of this afternoon trying to find where the water was and even pushed wire into the drain plugs to ensure that there was not anything stuck that could block the water draining out, but nothing found.

I will phone the manufacturer tomorrow to find out if he has any suggestions and will post the outcome tomorrow night. The figures have been double checked and they are correct.
I even had them weigh the boat on a different scale after the first reading but it was still the same.

thanks for all the help thus far it is much appreciated.

Maybe the big lesson here is that you never buy a second hand boat with out weighing it first, no matter how old it is.... expensive lesson

please advise us on what boat you have, motors etc!

Hi
It is an explorer 4,65 with 2 x mercury 40 motors.
Found out about another boat same make and length with the same problems and he had 80 litres of water trapped inside the hull.
I will go and see him tomorrow to find out exactly what he did.

Closed cell foam absorbs water I have pictures to prove.
My opinion is Sondor foam is the right way to go.

had a look at the boat here!

http://natalcaravans.co.za/explorer-465/

yip 700kg is too much!

I guess it's time to open up and see where all is hiding! that is, the water.

Call Grant Reed at Fibreglass and Marine, the manufacturer in Stanger, KZN. He has a great reputation and should give you sound advice on how to rectify the situation. This should be your starting point.

CraigT wrote:

Closed cell foam absorbs water I have pictures to prove.
My opinion is Sondor foam is the right way to go.

Click to expand...

Generally the first centimeter may be wet, but most of the time the core is dry.

Please post pictures, Id like to see it.

have to agree with Bennie here!

it is closed cell foam, so each bubble, cell is sealed of from the next one!

with the banging of the hull it could crush some cells, that's the reason why the 1cm or so could with water logged!

Thanks all for the input
Spoke to grant and he was very helpful and will resolve the issues.
there were differences in the weights of trailer and hull

benniejordaan wrote:[/quote]


"Generally the first centimeter may be wet, but most of the time the core is dry."

[/quote]





I'm busy taking the foam out of a 6 year old boat. There is lots of water in the foam. When pushing a wood saw blade in to the 500mm deep foam, and retracting it, between 350 & 400mm of the blade would be wet when pulled out of the foam. Tried this in different places. In the back half o the boat the result was the same at each location. Further forward it improved but there was always a wet area on the blade of at least 100mm.

The bottom +- 150mm of foam in the back half of the boat was saturated in area and soft like sponge. When squeezed water was expelled just as when you squeeze out a sponge. Its a pity i did not video it.

Admittedly the boat has been sent back to the builder several times for remedial work due to water in the hull, so the foam has been exposed to water, and I pretty sure that water has been in the hull for long periods between the attempted repairs.

The problem with foam in a boat with no bulkheads, is that once water gets in, whenever you use the boat it moves back and forth slowly wearing away the bottom of the foam. Once you get a piece of foam that breaks off and starts moving back & forth, then wear happens much faster. Take 2 pieces of PU foam and rub them together and see what happens.

I had a ski craft a few years back that had a foam filled hull, i had to cut a hole in hull to change some perished fuel lines and when i cut through the side of the fish box into the cavity the water came pouring out, what had happened was that the hull was not properly foam filled so the water collected between the foam and could not get out through the drainage plugs, and all along i thought my hull was dry due to no water coming out the plugs, so you could very well have the same situation. I font know how long the water was in there but the boat was around 7 years old, if the foam absorbed water then the water would have been in the foam and not between the foam, just something to consider!