Aluminum de25

[Rziel]

I just ordered boat building with aluminum so I have some studying ahead.

[jacquesmm]

It's a good book but it is not going to calculate the scantlings for you. For that, use Gerr's book and start with a much higher displacement than what I show for the DE25. It's not that my math was wrong but the boat was designed as a very light one and almost every builder added "stuff" . The final boats came out 1 or 2,000 lbs. overweight. They still perform well, just use a higher displacement in the scantlings calculations.
Many years ago, I surveyed new boats built in Al. The workmanship is very important. If possible, take a job with an Al boat builder for a few months.

[OneWayTraffic]

I think so too. But I'm not a designer, and would feel happiest starting with some valid specs. There's a lot of NZ boats built from welded aluminium, but design details are different. Gerr does have some lighter options in his book and a lot of differences from glass and wood. I would recommend the purchase.

Edit: This was a reply to Fallguy's comment on Gerr making a heavy boat, though I'm sure he'd prefer the term 'well founded.'

[fallguy1000]

Do you know that welding three corners into each other in a boat is an error?

[Rziel]

I have fabricated lots of stuff for commercial fishing boats. Hatches bull works trolling poles. But I haven’t build a boat yet. Hopefully some day. The first step is to find a lot and build a shop large enough.

[cracked_ribs]

Most NZ boats of that size have either 5mm or 6mm hull bottoms and 4mm on the sides. Surtees use 6 stringers, I'm not sure about the others. Gerr recommends 5mm hull with at least 25mm high longitudinals on 250mm centres. I know that there's a lot of other details on Aluminium building in Gerr's book, but I have the highlights in a spreadsheet. Most boats in that size are designed for motors and speeds much more than the DE25. I would think that if you use 6mm plate the boat would be very heavy.

1/4" (6mm) bottom, 3/16" (4mm) sides and six stringers would be about standard for an aluminum boat that size around here, all right.

You might get away with a thinner bottom if it's not going to see hard use, but it'd be pretty unusual in a boat that size. I've seen 3/16 bottom and 1/8 sides plenty of times, but only on small boats, or really cheaply built price point boats about a twenty footer.

That said, the DE25 probably has lower bottom loading than most of the aluminum boats built here, so if there's a boat that big that would tolerate a 3/16 bottom, that's a good contender.

[fallguy1000]

Keep in mind, a redesign includes power considerations. The boat is specified for 90-200. That is wide open afa speeds and forces on the hull. A 90 can probably wake jump, but the 200 can pound like crazy. Add trim tabs to keep the bow down and the boat pounds less.

Otoh, if you want to hang a 325 on it; something else entirely.

[Fuzz]

As Cracked ribs said 1/4 bottom and 3/16 sides is normal for around here. I think part of it is a little thicker material is easier to work with for home builders, not as prone to heat distortion. That being said if the commercial boys are not tearing up what you build that is a good sign you know what you are doing.

[BarraMan]

So why aluminium?

I can understand it for a rough tough bare-bones work boat but for a mainly recreational boat, give me glass/composite any day for ride, quietness and comfort. I assume the OP has aluminium skills and stitch and glue is a foreign concept - but one that is easily learned and produces beautiful boats.

If the answer to my question above is, "Because I want to", then I can't argue with that!

[cracked_ribs]

Glass has one set of advantages, aluminum a different set.

If you live somewhere with big tidal swings, active logging operations, rocky coasts instead of sand, and lots of thinly populated wilderness, aluminum is hard to beat. You can build them to ride well, also. In fact, I'd say it's pretty easy to compete against stitch and glue with aluminum. FRP out of a mould is harder to compete with for ride.

Aluminum is noisy and cold, though. But it's a lot tougher than glass, and in some places that's pretty important, even for recreational boats.

Here, most people with glass boats have them because they can't afford quality aluminum.