Aluminum hull advice

[thuss]

Thanks everyone for the great responses, I figured I'd be lucky to get one response on this thread!

Panope, enjoyed your video of you trying to break through that piece of 3/16" aluminum!

Cheechako, what's the difference between oil canning and a dent? By the way, like your forum photo. Our previous boat that we owned for 11 years and loved was a Hans Christian 38 Mark II.

[Cheechako]

Originally Posted by thuss

Thanks everyone for the great responses, I figured I'd be lucky to get one response on this thread!

Panope, enjoyed your video of you trying to break through that piece of 3/16" aluminum!

Cheechako, what's the difference between oil canning and a dent? By the way, like your forum photo. Our previous boat that we owned for 11 years and loved was a Hans Christian 38 Mark II.

well.... in my mind at least, oil canning is usualy caused by shinkage from welding or other stresses, bending the boat etc. The plates warp due to stress in the local area of the structure. A dent would be caused by impact. A dent would usually have stretched the material... so that it has more surface area than it previously did in that area. Whereas oil canning.. if you cut that piece out of the hull... it may return to being a nearly flat piece. It is stressed, but not beyond what's called "plastic deformation". It's still in the "elastic deformation" stage.

[Panope]

Glad you liked the Video.

I'll give an opinion that I have formed about boat materials. For me, the reason to have an aluminum (or steel) boat is not because of some (possible) increase in hull durability compared to fiberglass. The reason to go metal is because of the very large increase in deck and house durability and a corresponding lack of maintenance required.

With metal, you will have no soggy cores, no hull deck joint, no repetitive re-bedding of hardware. no leaks or wet bunks.

You can weld most hardware in a very strong and permanent way. Chain-plates, bow rollers, toe rails, bollards/cleats, stanchions, etc........can all be a welded, permanent part of the boat.

I have never owned a Fiberglass boat so I could be wrong, but it seems that fiberglass hulls are plenty strong and are very much maintenance free. Some Fiberglass hulls are as much as 1" or even 2 inches thick - solid layup!

Now, if a metal boat as been fitted out in the same manner as a "normal" boat (hundreds of holes in the deck for fasteners), than I believe one might as well get a fiberglass boat and avoid the nuisance of metal hull corrosion/electrolysis. I have even heard where somebody installed a teak deck on a steel boat with thousands of screws! The horror.

Here is another video that I created that backs up some of the above thoughts (rants?).

Enjoy

Steve

Fiberglass Test 1 - YouTube

[neilpride]

Got a question, this boat be in a hurricane pit hole, i mean , a hole where some yards drop the boat there resting in tires or sand bags ??

[thuss]

neilpride, no, she's been in Connecticut and in the winter stored either in the water or out of the water on her keel and jackstands.

[neilpride]

Ok,thx, i figurate , you know , sometimes boat stored in the hard for a while get damaged by jack stands , mostly in boatyards with soft grounds and crews not checking if the screws are tight or loose, i see that in Trinidad , lots of rain tend to sink the keel and the blocks in the ground where the jackstands are tight, oil canning and even in one boat i see close to 2 inches deformation ..

My boat is in the hard now, and i relocate the jackstands because the Yard crews are horrible at positioning jackstands, now every stand lay at bulkheads area, and i check jackstands every week, sometimes i release the screw sometimes i tight the stand...
Just a hint...

[thuss]

One other thing I noticed on this aluminum boat was that there's some white powder on the inside of the hull. The survey didn't show any issues with plate thickness but the surveyor recommendation was to sand down the white powder areas and prime it.

Here's a photo of a section where there's white powder on the inside of the hull, I'm wondering if that's normal or if that's something to be concerned about:

[OceanSeaSpray]

I have built a round bilge alloy hull in that size range and - honestly - not point over-analysing it. Ok, it is slightly dented between frames and you have access to the hull from the inside. Take a sledge hammer and see if it taps back out, it will depend whether the plate actually stretched or not. Anything more, remove the antifouling, keep the high-build epoxy that is well bonded to the metal, fair using an epoxy filler suitable for constant immersion, paint over with 2+ coats of high-build epoxy and cover with antifouling again.

Cracking is near irrelevant, aluminium cracks under repeated flexing, not from being dented. If the hull had hit something hard like rocks, you would see it very easily. There would be pressure points with conspicuous marks etc. Here it could have been caused by anything, from propping up and supports to landing on the turn of the bilge after broaching and getting dumped in a big sea. I damaged a fibreglass boat once in that same area in the southern ocean. Who knows?
The grade of materials is correct, the welding and workmanship are good, scantlings are adequate (what you have described here is typical of that size vessel, plating thickness could be a little bit on the light side, but it is also a question of displacement). If everything else is good and you like it, buy it. The dent is irrelevant.

On an alloy boat of that age, any significant problems would have had consequences by now.

All the best.

[OceanSeaSpray]

Originally Posted by thuss

One other thing I noticed on this aluminum boat was that there's some white powder on the inside of the hull. The survey didn't show any issues with plate thickness but the surveyor recommendation was to sand down the white powder areas and prime it.

This is common when aluminium is exposed to damp, salty conditions etc, like often in bilges. All alloy boats should have bilges painted at construction for this reason. I have seen workboats where pitting got so bad that entire plates were replaced. Yachts are usually drier and better looked after.
White powder alone is not an issue, but if you see deeper pitting, it has gone a little further. Even then, unless you are dealing with little craters that go deep into the plate, it is not worth doing more than stopping it.

You can sand (maybe) or brush (stainless steel wire brush, by hand) the white powder off, but it is not enough in itself. You need to chemically stop the corrosion. You can use an acid wash and/or an strong etch primer like Alodine. I have seen very sad-looking fishing boats that were treated with Alodine only and it stopped all corrosion instantly.

There will be other similar products around too, but whatever you do, it needs to chemically attack the corrosion, not just cover it. If abrasive blasting is an option, then it is ideal, but usually problematic inside a finished vessel.

[Cheechako]

Those look pretty crusty and not uniform throughout. I would scrape off some of those spots and see if there is any depth to them.

[sailnautilus]

Just to add a few thoughts....

We refit a 52' Kanter and have had her for 7 years. I would not be concerned about the "dents" but I do have significant concern about the spray in insulation visible in one of your pictures. The spray in insulation never remains dry and the contact between the insulation and the surface of the aluminum is the site of corrosion. We looked at many aluminum boats prior to purchasing ours, and peeling back the spray in insulation almost always reveals corrosion.

We had the most severe corrosion in areas of the diesel tanks where water lay trapped and areas of the bilge which were not coated. Areas of the boat which were coated properly with chromate and Interprotect were perfect even in a 15 year old boat. We ended up purchasing a sandblaster and doing a ton of prep work then either coating or calling the welder then coating...

Aluminum does have its detractions, but as was noted, also none of the hassles associated with fiberglass. After extensive work in the yard, I can tell you I would rather deal with aluminum repairs than fiberglass repairs, and this is my sixth large sailboat, first aluminum one. You can literally cut out a section, shape a plate and weld it in in very short time. Then a little prep and paint. Fiberglass boat owners with us in the yard are always amazed. From a cost standpoint, my experience has been that it is actually cheaper than comparable fiberglass work, and much quicker!!!

Our negative complications have all been related to the grounding and electrical systems, but with a little attention, these can be overcome. I will say we carry an extensive collection of Delrin washers and bushings and lots of Tefgel and caulk, as we never modify the boat without separating dissimilar metals.

For anyone who has not sailed a well constructed aluminum boat, they would be amazed (as I was) going below in my first gale. The wind can be blowing 45 knots and huge seas, and it is quiet as a church below. I was used to hearing the creaking and groaning of hull to deck joints, chain plates and general movement, even in a Hylas or an Oyster, but the experience is much different in an aluminum vessel. Gives you a real sense of security to see those huge chain plates welded to ribs in the hull.....

Best of luck searching for your vessel.