Thread: Goat Island Skiff

I know the plans call for 6mm ply, but I can get 5.2 mm oak plywood locally. Will it be thick enough for the GIS?

There are no 6mm marine plywood distributors near my little town. I'd have to order it and drive about 90 miles to ATL to pick it up. $64 a sheet, ouch!

Big German
Temple, GA USA

Hi and welcome!

That is actually a good price for 6mm Okoume, here in New Hampshire it is about $115 a sheet, in neighboring Maine around $95. I bought mine in the summer of 09 for $59, so you're basically looking at prices that are almost two years behind schedule. If I was living there, I'd jump on it even though I'm not building a boat right now!

Can the ply be shipped? Several yards around here will ship for a nominal fee. There are also online providers you could peruse.

Make sure it's not cheap Chinese fake stuff though.

The plywood is but a small percentage of the cost of building the boat. Using the material called for in the plans will not only benefit your boat, but it will be an investment in its longevity. Why get a plywood that risks rot and/or delamination in a few years that will threaten the entire sum of money that you sunk into the project?

To be totally completely honest, if you want to find cheaper alternatives to the cedar framing, (like Doug Fir, or maybe Pine-- check with Mik on that one) that would be better than skimping on the plywood and you'd probably almost make up the difference since cedar is so darn pricey. Since everything is encapsulating with epoxy, the framing will be fine. You can't get in between layers of ply though.

You spent premium money on a set of plans that will deliver a capable, fast, lightweight boat that will last a long time if correctly built. You might as well make it worth your while!

Howdy,

I am not sure what sort of oak it is, but most are very heavy and some are very difficult to glue.

main problem is that the gaboon gives a boat that is not too hard for two adults to move around on shore.

an oak one might be up to 50 or 60% heavier.

best wishes
MIK

Be careful with cheap ply. I had an awful experience when I started building my GIS. I thought I got a great deal on some Okoume at about $60 per 4x8. It turned out to be China crap that had footballs in the outer veneers. The grain looked ugly, kind of like the cheap Louan at Home Depot. If you don't care about appearance or are planning to paint the boat inside and out then the cheap Okoume is probably OK. I ended up buying the French Joubert brand which is the real deal. It was $83 per sheet and is flawless. Well worth the extra $23 per sheet or $138 total for 6 sheets.

GIR was weighed today. All up weight which includes everything to go sailing, all lines, pulleys, sails, battens, oars, rudder, daggerboard, tiller, and mizzen rig.

Yawl Rigged: 262lbs (119.09k)
Lug Rigged: 253.6lbs (115.27k)

Mizzen: mast, boomkin, sprit & lines: 8.4lbs (3.82k)
Oars: 9.4lbs (4.27k) 4.7lbs each. Is that a heavy oar?

So if I took the oars and mizzen rig off the boat I can get down to: 244.2lbs (111k)

Not bad for a 15'-6" boat!!!!!!

I've been meaning to ask this question for ages. What causes the hull to hum just before it planes? It's a definite harmonic rather than a vibration. Does anyone else have this?

I was wondering if it has anything to to with the squared off trailing edges on the foils?

Howdy,

It is likely to be the foils. You can often make it disappear by angling the trailing edge slightly - maybe 30 degrees rather than perpendicular to the centreline. It means the vortices coming of the trailing edge are likely to be out of harmony.

It could also be amplified by some other part of the boat having the same harmonic like the soundbox of a guitar.

MIK

Thanks MIK. The funny thing was that it wasn't evident today. I'll try moving the CB next time, although I don't have much room to play with as the case is pretty tight around the board.

Hi woodeneye. Your reply suggests that maybe you misunderstook MIK. I think he was suggesting physically altering the trailing edges of your foils, rather than changing the orientation of your foils to the water.

It's often recommended to leave a square edge a couple millimeters wide on the aft edge of foils, rather than a sharp knife edge. I think what MIK is suggesting is rather than having that trailing edge face precisely square to the fore-and-aft axis of the foil, angle it to one side something like 30 degrees. So instead of a knife, it's somewhat like a very blunt edged chisel.

Just a guess. Right MIK?
Grant

Oh OK, yes I did get the proverbial cat by the tail didn't I?

Originally Posted by Old Yeller

Hi woodeneye. Your reply suggests that maybe you misunderstook MIK. I think he was suggesting physically altering the trailing edges of your foils, rather than changing the orientation of your foils to the water.

It's often recommended to leave a square edge a couple millimeters wide on the aft edge of foils, rather than a sharp knife edge. I think what MIK is suggesting is rather than having that trailing edge face precisely square to the fore-and-aft axis of the foil, angle it to one side something like 30 degrees. So instead of a knife, it's somewhat like a very blunt edged chisel.

Just a guess. Right MIK?
Grant

Spot on Grant,

The template and the foil thickness interact to give a slightly wider trailing edge on the centreboard - after all it is a cruising boat, not a delicate racer! The rudder trailing edge is unlikely to hit anything (it is a bit hard to back up at high speed) so it is close to widths you mention.

But like a chisel that is unbelievably blunt! Like 20 or 30 degrees off having a perfectly square trailing edge.

MIK

OK, another item added to the winter maintenance list.

Howdy,

The slanted trailing edge is a quick fix - just to put the harmonics out of phase.

I have noticed in the past that a non humming board can be turned into a humming board with a leading edge imperfection from bumping the board, so I would look at that too

MIK

Just to lighten up ... a video or two ... they have appeared one place or another in the forum already, but I was just reviewing to see if there were any more videos to add to
YouTube - boatmik's Channel

... and I saw this again. The camera boat is moving in the same direction hehe

[ame="http://www.youtube.com/watch?v=g2yYiZJxREM"]YouTube - 100_0033.MOV[/ame]

MIK