a one-off bow extension

[CDK]

It may be that my joints get stiffer or it is just the sea-level rising. Anyhow, stepping on board is getting harder, so I want to replace the hardwood and stainless steel tube with an anchor board that has an extra step. To be made from grp, the fixed part hollow, the folding step neatly finished on both sides.

Do I make a plug from wood and plaster first, then a female mould from polyester or just make the mould from wood and some polyester filler to round off the edges? And how do I create an anti-slip pattern on the surfaces that will be stepped on?

[marshmat]

Hi CDK,

I take it you moor bow-to-the-pier a lot? If so, I think a step like this might be really handy, provided you can figure out how to work the stainless steel bow rail around it.

It's a relatively simple shape and is a one-off part, so if you really want to do it in fibreglass, the easy way is probably to use MDF or plywood to build a female mould. Bondo or similar works wonderfully for rounding off the inside corners. I've done a lot of solar car parts this way, and with careful construction and a suitable finish layer, simple MDF moulds could be made sufficiently vacuum-tight to bag prepregs at 80+ celsius. For simple shapes only, of course!

The best non-skid I've ever walked on was also the simplest: nothing more than coarse silica sand, sprinkled liberally onto the second coat of primer while it was still wet. Brushed the loose sand off the next day, rolled on two layers of topcoat, and presto- cheap, grippy, easy to clean. A bit of masking tape around the edges and fittings before laying down the primer and sand, and you can't tell the difference from an expensive, tedious moulded-in nonskid.

[CDK]

Thank you Marshmat. The non-skid solution is a splendid idea.

I've already made a large radar stand and the transom extension with female moulds, but found the rounding off very time consuming.
What is Bondo?

[Frosty]

I found that sprinkling gives an uneven finish. I uses 'fine' silica sand mixed in to paint of your choice and dab it on with a brush. I was very pleased with the very even finish.

No it doesn't come out of suspension and occasional mix is all thats required.

If you use a 2 pack it can be stored.

If you do mix it in the paint take note of the quantity and use a tablespoon to measure the spoonfulls of sand so it may be repeated for maximum evenness.

[marshmat]

Bondo = a cheap, easily sandable, car body filler. Not waterproof or vibration-resistant enough for boats, but it works wonderfully for moulds.

For a one-off mould, PolyFilla or drywall compound works, too. You can get some beautifully sculptured curves with five or six layers of drywall mud, followed by some smooth finish that you can wax and polish. Such a mould won't survive more than two, maybe three parts, though.

Frosty, how do you get the sand to mix into the paint without making it too thick to spread? Are you using a lower viscosity paint, or thinning it a bit?

[Frosty]

Yup tis pretty thick, thats why I dab it. Its not a fast application suitable for a professional yard but for DIY I found it to be very satisfactory, slow but entirely in control.

1 Sq meter 15 minutes!!

[mydauphin]

Excellent thread... sweet and to the point.

[rwatson]

If this is a one off product, I wonder why not carve some Urethane foam into shape and cover that in FG. The foam wont add much weight but will ad strength, and will make the whole manufacturing process easier.

I would suspect it will be a much easier job of fairing the whole thing on a male component than a female shape too.

[CDK]

This is today's result. Not as smooth as I'd hoped, but very functional (patience never was my middle name). Two coats of 2-component polyurethane can do miracles.
My neighbor says the non skid surface is so coarse people might get hurt when they slide off with wet feet, so he clearly didn't understand the function.

Mydauphin, thank you the big compliment, resulting in a 5-star rating.

[marshmat]

Looks pretty good from here, CDK
Your neighbours at the slip, of course, will all be going "WTF???"
Until, that is, you give it a little kick and step gracefully onto the dock without having to hang off the bow rail like a monkey....