Best method to increase buoyancy to GRP tender?

[conks01]

Hi.

I have an 8' fibreglass tender which I'm restoring and I'm looking to increase buoyancy to as it rolls.

Can anybody make a recommendation as to the best method to do this please.

Thanks

 

[ghostlymoron]

If you mean to stop it rolling you'll have to fit outriggers. If you want to stop it sinking, flotation bags under the thwart or side seats as in a sailing dinghy would do or glass in some air tight compartments. I suspect you want the former. Nothing you can put inside will help,I'm afraid.

 

[ShinyShoe]

As ghostly says - roll wont be helped by adding buoyancy inside. A few things might help a little. Ballast low down - so oddly enough as weight at the bottom centre - concrete or resin and metal have been used before.

Where are the current thwarts? Any scope to lower them? Lowering them would reduce your COG too.

What goods do you carry? Are they low down?

But if roll is really an issue you need to either modify the hull shape or add some external buoyancy. Option L here: https://www.sailmagazine.com/diy/fenders-for-your-tender for fendering would be my first try... a string of fenders on each side with each fender attached individually fore and aft to below gunwhale if possible. Effectively you are creating a RIB. The only way to submerse the side is to submerse the fender. I think it looks functional without looking like you should be given a wide berth. 8ft boat with 8 or 9 27cm x 8cm fenders on each side (not big), cost £100 if you shop around. Probably adds about 80N of buoyancy per side So a person stood on the side will still manage to dunk it. Not enough? Go up to 18cm ones if need be and get up to 400N per side.

This guy has achieved similar: https://eoceanic.com/sailing/tips/13/206/additional_buoyancy_for_the_'hard'_or_'traditional'_tender/ but they all look a bit "special"

 

[lw395]

Sometimes you can improve the roll behaviour of small tenders by careful placement of your weight, fore and aft, also maybe lower?
A lower thwart might help.
Some tenders which are popular around Portsmouth are much better if you sit in the middle of the boat than back with the engine one-up. A tiller extension is good.
People buy 'boat shaped' tenders because they look 'nice', but a boxy looking thing has more stability.
For buoyancy in the event of being swamped, some GRP boxes built in is probably the best.

 

[TQA]

The US made Walker Bay uses an inflated collar fitted around the gunnels.

It has similar problems with minimal buoyancy and stability issues.

The collar is quite expensive and I have seen penniless cruisers use pop bottles held in a tube made from recycled fishing net on their tender tenders.

 

[Billows]

Sell it and buy a Chinese made inflatable tender

 

[William_H]

Around here the kids have what they call "noodles" for swimming with. Basically a foam tube about 1.5m long with foam about 2cms thick with outside diameter about 5 cms. These could be attached to the outside of the hull just under the gunwhale. Possibly 2 each side one above the other. This will provide buoyancy when the gunwhale dips down but will also make a great fender. Very cheap. https://www.kmart.com.au/product/pool-noodle---assorted/948329
ol'will

 

[ShinyShoe]

Noodles - you may find birds like to peck them and depending on how much its used as a fender will need replaced quickly. Use as a fender may not be in your control of you leave it alongside others...

PLUS -

8ft of 5cm foam (in the UK they are "solid" foam noodles rather than tubular...) - actually only gives 15N of buoyancy per side.

 

[ghostlymoron]

My minipram 10' is pretty stable as it's flat bottomed not round bilged. Doesn't row badly either and has two built in bouyancy compartments and two sets of rowlocks.

 

[ffiill]

Follow the mirror dinghy route.
Replace middle and stern thwarts with glasses in plywood boxes and and one to bow.Add some watertight round hatches for storage access.
I did this on a little pram I found derelict almost 30 years ago and it's still alive and kicking.

 

[ghostlymoron]

That won't alter the 'tippiness' of a round bilged dinghy unfortunately. It will stop it sinking.

Follow the mirror dinghy route.
Replace middle and stern thwarts with glasses in plywood boxes and and one to bow.Add some watertight round hatches for storage access.
I did this on a little pram I found derelict almost 30 years ago and it's still alive and kicking.

 

[greeny]

Follow the mirror dinghy route.
Replace middle and stern thwarts with glasses in plywood boxes and and one to bow.Add some watertight round hatches for storage access.
I did this on a little pram I found derelict almost 30 years ago and it's still alive and kicking.

If you use them for storage it may be best to only put light things in there or the buoyancy will be negated by weight and become ballast and you may as well not have it.