sorry not related to the merlins but how come some people say you need to antifoul dorys which are in fresh water and others say its not necesary

sure some of you gurus know the answer

There is a good freshwater antifouling called "Broads Red" obtainable from Jeckells at Oulton Broad amongst many others, however a dory being light you could surely pull it out every so often (3 week intervals?) and pressure wash or hand wash to remove the slime. You'll need to wash the outboard through anyway.

Fresh water can have green algae, and it can make a real mess at waterline.

sorry to be a tad thick but was thinking that there are 2 issues slime and osmosis, does the antifouling deal with both of these

guess we are wee bit lazy and leave it in the water a lot

Osmosis is water ingress through the gel coat,that capilarizes up the glass/kevlar/carbon strands, with obvious results, clean back to sound gel coat, let dry covered outside or in an airy shed for quite a while and apply epoxy or other recommended paint (two coats at least.) Then antifoul over top antifoul is only to prevent fouling. Frankly Dory Hulls are so inexpensive I'd have thought that if you have osmosis in a dory hull junk it and canabalize the fittings onto a new one. Getting rid of osmosis is a long b***ls aching job. Getting a good smooth finish later even more so, however if you just wish additional protection the above is fine, various "Interspray" shops attached to boatyards will do it but once Dory & Dinghy Hulla are hardly costly enough to justify the expense.

ok thanks

gues i wasnt  sure why all keel boats sailors put it on as a preventitive measure an ddory people

is it just a cost issue re value of hulls

Not all keel boat sailors by any means use anti fouling a great many dry sail that is to say crane in only when racing, osomosis is a rare problem on modern plastic hulls and all reputable manufacturers offer a 10 + guarantee. Non the less all GRP hulls should; if possible; spend at least 4 months a year out of the water and be allowed to dry off properly. Though lots do not and are OK. Anti fouling is solely to prevent fouling; that is say slime, green stuff, weed, gribble worm, toredo etc., which it does to varying extent it is poisenous and should never be dry sanded off, there are a few non-slip non toxic antifoulings now and the better Merchant Ship Operators are using it as well it works just like a non stick frying pan making sticking harder and cleaning easier. There is roumoured to be a performance improvement but as yet undemonstrated - commercially any way. Any boat or ship left in the water will need regular cleaning around the water line with a mop, squeegee or similar. The more toxic antifoulings such as TBT are now banned (They do strange things to the sex life of Dog Whelks amongst other things.) There are also some copper compounds -poweders that are mixed into gelcoat when a GRP Hull is first moulded that are anti fouling and need only a light sanding every year to renew efficacy, they can be "retrofitted" by painting onto wood or GRP hulls but need pretty hard cutting back initially to smooth and expose the copper grains. The RNLI have used this. So have a few boat builders, it works.

thanks thats clear for me

And if your Dory lives on a fresh water reservoir then I believe the water company may get a little unhappy if its got anti fouling on...

It will. Wise warning!