Aluminum hull advice

[thuss]

I just had an offer accepted and had a survey done on a 47 foot aluminum sailboat built in the early 80's. Boat was built by a big reputable aluminum boat builder. The ultrasonic/audio-gauging testing came up relatively clean showing suitable plate thickness (good). But found some bending of the 3/16" hull plating between the frames (bad, photo attached below). The hull is 3/16" plate down the keel and 1/4" on the keel. Surveyor thought it could probably just be faired and painted over since the plate thickness is still ok.

This would be my first aluminum boat (owned large fiberglass boats before) so I'm looking for opinions on whether this is the type of issue where this just happens on aluminum hulls sometimes and it's probably ok or whether you just walk away because it's probably indicative of larger problems? I know there's no definite answer so wild theory and speculation encouraged!

[neilpride]

Looks Like Jackstand to tight by previous owner?? I see something very similar in a long alu ketch,, Penduick VI , but here for the effect of wave pounding .

If the inside framing and plates are ok, you could use a suction tool to pull the plates in place maybe??

[Panope]

If this is just as it seems - hull plate pushed in a bit, then I would not give this a second thought. Just go sailing - you will never know those bends are there.

If this is part of a larger problem (such as plating that has been replaced and warped during overzealous welding), then you should dig a little deeper to make sure the repair was done properly.

If the dents are basically the same on both sides then my guess is same as neilpride's - too much pressure on jack-stands.

Panope does not have any "dents" but she does have (always had) some light warping (skinny dog look) between frames. Boat as never been faired so these kinds imperfections are normal to me.

Steve

[homeless]

There is another aluminium boat for sale at the moment in the US with similar damage. Broker admits it was knocked off the stands during a storm, but says it is purely cosmetic. Pictures of the inside of the hull show a shiny new frame in that location (made from checker plate!) and the sprayed insulation is a different colour indicating it is new, so the damage was more severe that the owner/broker admits, and the repairs were definitely not done by a professional. Any damage in an aluminium boat can be repaired, but if they lie to me about something so obvious then I can't be sure what else they are hiding.

Ask your surveyor if they were able to check the frames and welds in that location.

[thuss]

Thanks for the great responses, it hadn't occurred to me it might be jackstands.

Does 3/16" plate seem suitable for the hull of a 47 foot sailboat (1/4" on the keel)?

Thanks,
Todd

[thuss]

Originally Posted by homeless

There is another aluminium boat for sale at the moment in the US with similar damage. Broker admits it was knocked off the stands during a storm, but says it is purely cosmetic.

Homeless, that boat you mention doesn't happen to be a pilothouse that's for sale in Connecticut does it?

[bdbcat]

thuss...

3/16 seems right for this size boat. What is the frame spacing? What is the weight overall?

I've owned a large aluminum power cat for 12 years now. 50', 35 Tons, 3/16 plate. Some plate dishing built in, some caused by rough handling ashore and afloat. I consider the dishing to be cosmetic only. I definitely would not fair over it. Just sail it.

Were I buying a used alloy boat today, I would focus mostly on the bliges. Look for evidence of plate thinning and coin-sized divots caused by corrosion coming from little tiny bits of copper and/or steel sitting on the plate while partially wet. Very hard to avoid over the long term unless you keep dusty bilges, which is a near impossibility on an actively cruised boat.

Become an anti-copper zealot onboard. I give all my pennies to my grandkids

Dave

[Panope]

Originally Posted by thuss

Thanks for the great responses, it hadn't occurred to me it might be jackstands.

Does 3/16" plate seem suitable for the hull of a 47 foot sailboat (1/4" on the keel)?

Thanks,
Todd

Panope is 3/16" plate through out. Seems plenty stout. She is 34 feet on deck and displaces 7 tons. I have never thought of her as any kind of ice breaking, shipping container crusher. Then again I haven't really crashed her into anything.

Here is a video that I created for another thread last year. No science, just some vigorous smashing.

Steve

metal test - YouTube

[homeless]

Originally Posted by thuss

Homeless, that boat you mention doesn't happen to be a pilothouse that's for sale in Connecticut does it?

The boat is listed in Texas, but the listing may be wrong. The attached picture shows what seems to be a frame repair made with checker plate. It may be stronger than the original frame, but doesn't give much confidence that it was done professionally, and when combined with the overall state of the boat I won't be making an offer

[Sharkman]

Hi

While you may well be right to just walk away from this boat, just looking at the dents and the repair, it doesn't look as if there's a colossal amount that couldn't be repaired relatively easily, at least on the face of it.

It would be far better to try and panel beat or pull out the dents than fill and fair, which unless it's done with real care can cause more harm than good in the long term. It would also be interesting to check whether the aluminium stiffener in the pic is of a compatible marine grade alloy to the rest of the structure, and that the correct grade of rod etc has been used.

Even if the above had to be done/re-done the costs shouldn't be astronomical, and as the cost of the repairs should be deducted from your offer, it might still make a good buy for someone, as long as the rest of the boat is sound.

C

[Lagoon4us]

If there is no other buckling on the underbody i would suspect AND inspect the following:-

1) Are there any cracks on the frames/stringers inside in those places and say a metre all around.

2) From the inside can you see any repairs that have been done.

3) On the inside are there any mountings etc placed in those area's i.e. framework for the side stays as it looks like an over-compression issue that's transferred load down SO is this in line with a mast compression post?
What i'm seeing is quite possibly the results of buckling from '"a fully welded area" which makes sense if it's supporting or connecting to the compression area.

4) Has the rest of the hull underbody been filled and this was where jackstands prevented filling to be completed?

Hard to say from limited picture but just check those points.

Cheers Frank

[hpeer]

I have more experience with steel than aluminum but agree mostly with Sharkman above.

Unlikely the diamond plate is of correct alloy, amateur repair. That being said it is likely not a problem because it is up out of the water.

We went to closing but then walked from a 43' aluminum schooner because of shoddy welding. That boat was 1/4" alloy. Good and interesting design, poor craftsmanship.

To my mind the fundamentals of a metal boat are real important. Who built it? Backyard or pro? Who designed it and can you get the origional scantlings? Some designers, such as Ted Brewer, are very accessible and will consult for a very reasonable fee. Nor does it need to be the origional designer. you could check with the Metal Boat Society for a referral. I would be very cautious of home built boats.

http://www.metalboatsociety.org/

3/16" may be fine, or may not. We looked at steel boats from a Colvin Gazell to a custom steel Fisher. Both 44', but the Fisher was over twice as large as the Colvin, easy. Scantlings were proportionately different. So it is important to check the origional design. I saw a 50'ish Colvin out of 10 gage steel, that was thin.

Our 44'er is 1/4" keel and first two plates, then 3/16"---steel. A veritable tank. The 33 is 10 gage. Both are appropriate to the size of boat.

FWIW, if you can look at the welds on the ribs/ stringers ...they should have a 2" weld on the left, 2" no weld, 2" weld on the right, no weld, repeat. Hope that makes sense.

I would not worry too much about the dents. I have seen far worse. That is why we love metal boats, not for the beauty, but for the soul. I did worse to our 44'er last summer. Got caught on the wrong side of a ferry dock in a 50 knot blow. 2-1/2 quarts of Bondo later, mixed liberally with embarrassment, and all is well.

[noelex 77]

The dents don't look too bad.

With the location I would suspect the boat has laid over on some rocks. This sort of damage is typical in high tidal areas where the boat leans over following a grounding. Similar on both sides is unusual, but its possible the boat fell onto opposite side, or there were a couple of grounding incidents.

As always check the basics
Grades of aluminium used
Quality of welding
Frame spacing.

[thuss]

Thanks for the all the great responses! The dents are accessible from the inside of the hull so the surveyor was able to verify that no welds were affected. In terms of the spacing the survey reports:

Construction is 3/16” aluminum plating over aluminum formed frames and longitudinals. Frames are tee section sided 3”X 3/16” on 16” centers. Longitudinals are 11/2”X1/4” on 8” centers. All welding is to ABYC standards non continuous. Plating is 5058 aluminum with welded butt joints.

[Cheechako]

Hard to tell if it's dents or oil canning. Good advice above regarding checking for repairs and damage. Frankly, if nothing is wrong with the boat but the ripples... just go sailing.... When I built alum powerboats the 24 footer was 1/4" plate on the hull bottom! However, my marine architect said he once built a 100 foot ferry with 1/4 plate... so you're probably fine with the 16" frame spacing....