Aluminum boat rebuilding project - The Vonda Lynn

Discussion in 'Metal Boat Building' started by cthippo, Jun 22, 2020.

  1. bajansailor
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    bajansailor Marine Surveyor

    I don't think it will do that on it's own - but it will be a different story when you and your crew are on board and underway, and you have wind loading on the side, and you decide to make a turn and the boat starts heeling outwards - it could get a bit dicey then.

    CT, folk on here are trying to tell you how it can be done - and they don't think that what you are proposing is very sensible or safe.
    Please take note of what they say. Especially so the link with the boat where they removed the house, and the boat was transformed for the better.

    Little open speedboats were never designed to carry ungainly sheds on top of them, along with crew weight high up (rather than low down as it would be in speedboat mode).
     
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  2. fallguy
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    fallguy Senior Member

    A couple of things you could do differently.

    First. Find the rating plate on the Starcraft and take it seriously. I estimate the rating plate to be about 1500 pounds persons, motors, gear. Engine of 200, battery bank of 100, fuel tank and fuel of 200, scuba gear etc of 100, pax of 700, misc of 50 and you are at 1350 no wheelhouse which affords you 150 pounds of wheelhouse. All your mods add or subtract as well.

    Second. Recognize a full height pilothouse built from aluminum is too heavy. A half height ducker is still too heavy most likely, if aluminum.

    About the only thing you could build enclosed is a foam sandwich ultralight top ducker which might get close to the 150.

    I am sorry to be the harbringer, but the purpose is to avoid loss of life, a fairly serious construct.

    You do realize the CG has a responsibility to not allow dangerous vessels? They have to do so to protect people who unwittingly climb aboard a dangerous boat and to protect others from saving those folks when they need it. If I board your vessel, I'd not allow it.

    Most people who post boat mods here and get strong criticism reject it and they leave; sometimes wisdom kicks in.

    I apologize I checked out of this thread awhile ago and that I did not tell you the idea is 100% wrong. You may be partway into the build.

    It is a mistake.
     
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  3. cthippo
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    cthippo Senior Member

    Tons of progress today.

    I spent new years day figuring out how to join beams with riveted gusset plates on inside corners in multiple planes. The answer I came up with is slotting them together like IKEA furniture and then riveting them to the beams. I've been very happy with the results and if at some point i decide to sell my soul to the devil for the knowledge of how to weld aluminum I can go back and weld up the riveted joints.

    https://www.boatdesign.net/attachme...3/?temp_hash=91477b73a9241612a29c0f73adc456f9

    The forward cabin is mostly done, but I decided today to go back and re-work how the aft wall attaches to the structure of the vessel and reinforce it some. This will mean taking up and re-cutting the deck grating and re-working some of the structure I already have in; It's going to add a couple of pounds of weight in the bilges, but I think the increase in structural rigidity will be worth it. I'm also going to reinforce the subfloor to take seat mounts while I am at it. Right now i'm at that point where sub assemblies start coming together and some stuff just has to be figured out when it is next to the piece it connects to. Not looking forward to playing with the fiberglass grating again, but it should be just some trimming. At the rate we might be splashing this month, amazingly enough!

    https://www.boatdesign.net/attachme...2/?temp_hash=91477b73a9241612a29c0f73adc456f9
     
  4. bajansailor
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    bajansailor Marine Surveyor

    Your progress is commendable, however there is a big but - are you confident that the stability will be ok?
    Fallguy makes very valid comments above.
    Can you post a photo (or two) please, showing the forward cabin in place?
     
  5. cthippo
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    cthippo Senior Member

    It's a guess, but i think stability will be ok. The weight of the cabin is actually not that much. I can't give you a number, but I can pick up the wooden mockup by myself without trouble, and so far the solid wood is proving to be heavier than the hollow aluminum. I had originally planned on doing sheet metal for the skin, but I am going to price the plastic sheets my friend used on his pontoon boat which have stood up well despite many thousands of road and river miles. The bulk of the weight will be aft of where the hull becomes full volume, and will be counterbalanced fore and aft by the stupid heavy motor. There are also going to be some movable weights such as batteries and fuel which can be placed in different spots in the hull to balance out trim issues.

    I'm building this very much like a camper shell for a pickup in that while it bolts on, it can also be removed. If it turns out to be too ungainly I can pull it off, recycle the metal into the next project and sell someone a fast open runabout that I have no use for.

    I'll try to post a couple of photos of either the mockup or the framed cabin tomorrow depending on the weather. Been enjoying working on the cabin in the shop and not looking forward to getting to the stage where i have to go work outside again!

    I'm tempted by this thing for my next project... https://portland.craigslist.org/mlt/boa/d/gresham-19-ft-all-aluminum-inboard-boat/7255252696.html
     
  6. fallguy
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    fallguy Senior Member

    The one with the inboard looks bigger. But so many of these older boats have narrow beam the displacement is insufficient for large mods. But that one looks better suited for your plan.

    If you could find an old Bertram moppie; they wpuld be less weoght sensitive than the Starcraft, and you could even build a dive door.
     
  7. cthippo
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    cthippo Senior Member

    The construction looks super similar to the Starcraft, I wonder if it's not also a SC.

    I'm not sure I want a glass hull, though they are more readially available. Some of the native crabbers do interesting things with old glass powerboat hulls and i suppose with enough backing plates it really doesn't matter, but...

    Someone had a whaleboat in their front yard for sale, but it disappeared before I could take a look at it.

    Of course, the end all and be all would be to salvage a derelict and rebuild it. Hmmm...
     
  8. cthippo
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    cthippo Senior Member


    Haven't gotten much more done as this has been quite the week in my world. My big accomplishment today was actually tearing down and burning the wooden mockup as it has fulfilled it's purpose and is literally falling part.

    I've attached (I think, this site uses a weird attachment system) pics of the mockup and also of the builder's plate, which i found today. mas capacity is a couple hundred pounds over Fall's guess, so I have some room in the weight budget.

    Next step is to pull up the floor gratings and install a wider and stronger transverse member that will support the rear cabin wall. Originally I was going to have it sit on the grating, but have decided that adding a full width stick of tube will add significant rigidity for minimal weight. Unfortunately, one change means everything else has to change, so...

    I did get a quote on 1/8" PVC foam plastic and acrylic and will probably end up going that route for the skin of the walls. After the skin is in place I will add external gusset plates for further reinforcement.
     

    Attached Files:

  9. fallguy
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    fallguy Senior Member

    I guessed 1500# rating and I see 1500# rating on the plate.

    where am I off by 200#?

    1050 persons affords 450 for engine, fuel, and batteries, no?....plate impossible to read
     
  10. cthippo
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    cthippo Senior Member

    For some reason I remembered your guess as being 1300. My bad.
     
  11. cthippo
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    cthippo Senior Member

    They say the darkest hour is just before dawn, and on this this project it's kind of true. I'm back to a bare hull, but only briefly. A few design changes in how I'm mounting the cabin required me to go back and change the subfloor pieces, and in doing so I realized that the top of the stringers are half an inch below the corresponding mounts on the hull. This wasn't an issue until I reinforced the transverse member that will form the base of the rear wall of the cabin and it stood, you guessed it, half an inch proud of the stringers. OK, another trip to the aluminum store for some 1/2" x 1" bar stock because, as they say at Boeing, Shim happens. In the long run this adds some weight, but it is way down in the bilges and should contribute significantly to over all structural rigidity. Once the shims are in, things will start happening quickly as most of the other subassemblies are done and waiting to go in. I will hopefully get the transom in tomorrow so the 5200 can start going off, followed by the subfloor assemblies, and then the decking.

    Speaking of the subfloor assemblies, they have grown in complexity and rigidity. One of the big questions I hadn't figured out was how to hold down the grating in the floor since once it is in place I can't reach the bottom to fasten it, and I don't want to thread into aluminum if it can be avoided. My solution was Tee nuts, which are riveted into place on the underside of the transverse members and then I can run bolts with fender washers down from the top and thread into them. This way the bilges are always visible and can be reached by just removing a couple of bolts and popping up the grating panel if need be.

    Once the floor is complete the two rear wall sections can go in, followed by the forward cabin structure. I will have to make some custom gusset plates to join those since i don't yet know where they will line up, but that process is pretty much down to a science at this point. Then it is just a matter of cutting and installing the roof pieces and we will be ready for skin.

    Might be able to get it in the water with the 4HP motor next week just to leak check it and establish baseline stability before adding the cabin. I'm going to hold off on adding the 90HP motor on until quite late in the process because once that two stroke monstrosity goes on I am more limited in where I can use it and the convenience of being able to pop down the road into the local lake for testing is nice.

    Once the frame is done, the next big project is the dash. i intend to install hinged drop down dash panels so that as my electronics suite evolves I can easily change out systems. Also, some of the systems are not what you would call "marine grade" and so may come indoors when the boat is not in use. In addition to the steering and throttle I am leaning towards a PC based primary navigation system, my existing Garmin sidescan unit for the sonar and installing a PC monitor for the underwater camera system.

    Little by little the process continues.
     

    Attached Files:

  12. cthippo
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    cthippo Senior Member

    Much has been done in the last few days!

    The subfloor has been permanently installed except for the seat bases, which will have to wait until I get the seats themselves and figure out how that is all going together. With the subfloor in place it was time to assemble the cabin sections and make the gusset plates that hold them together.

    The last step of the cabin frame is the roof and while I had originally planned to go with a beveled design seen in the mockup, my friend suggested a curved roofline with rectangular tube. We have a roller bender we built for another project that could bend 1/2" x 1" rectangular tube bows for the roof. This would not only be lighter than the gusseted tubes I had in mind, but also protrude down into the cabin less, reducing head strikes. I think I like the aesthetics of the beveled roofline, but the advantaged of curved sound pretty compelling. Open to thoughts on this one.

    Next task is probably the dashboard while I figure out what to do with the roof.
    20210124_145727.jpg 20210124_145741.jpg 20210124_145756.jpg 20210124_145819.jpg
     
  13. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    Dang, where I live a boat that size and weight will be submerged on its side in the first summer windstorm.. Not enough weight to resist tipping over due to the wind forces on the superstructure.
     
  14. cthippo
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    cthippo Senior Member

    Fortunatly we don't get winds like that often and it will live on it's trailer when not being used.
     

  15. cthippo
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    cthippo Senior Member

    Turns out the curved roof isn't an option. I can get the tube to support it at a nominal cost, and have access to a bender, but the sheet metal to make it from one piece is just not available. My supplier can't get 6061 sheet at any price, and might, emphasis on might, be able to get 5xxx alloy in 6' wide pieces, but at a prohibitive price. So, beveled roof it is. I'm changing up the design a little on the roof supports out of concern for fore and aft racking, but not a huge amount. Really exciting how fast this is coming together. Should have it out on the water for initial testing next month!
     
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