Transom reinforcement question

Discussion in 'Boat Design' started by ballfeng, Mar 3, 2022.

  1. ballfeng
    Joined: Mar 2022
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    Location: CA

    ballfeng Junior Member

    Hello, first time post. I have a project that me and my father has been working on for a few years now. It was hard as he is getting older but really want to ride the boat before its too late for him to enjoy it so, I decided that I need to get the project done, asap.

    First of all, the boat is a inboard Customweld 18' with Viper motor and Jet propulsion. My father wanted more room inside the boat so we took out the motor and ordered a Honda outboard.

    While looking at the placement of the motor, I'll have to design a bracket for the mount and this is where I'm stuck. I can weld and fabricate but I don't have the knowledge to be sure the mount will hold the 150HP outboard. The transom is only about 1/8" thick so for sure we'll need to beef it up. Any idea on how to tackle this would be of great help. I have pictures of what I made so far but I don't know how to upload on here, yet. I would love to see the smile on my father's face when it's done!
    Thanks everyone.
     
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  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum Ballfeng.
    Re your boat, how old is she now? Is she similar to the one in the link below?
    19’ Viper Series https://www.customweld.com/recreational-boats/19-viper-series/
    How much power did the water jet have in your boat?

    Re your photos, it seems to take a while before new members are allowed to post photos. If you would like to email them to me, I can post them for you if you like.

    Re the 1/8" thick transom, have you welded up the hole where the water jet unit was?
    If yes, do you now intend to hang the new O/B motor on the transom, or build a pod bracket standing off the transom?
     
    Last edited: Mar 3, 2022
  3. ballfeng
    Joined: Mar 2022
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    ballfeng Junior Member

    Hello, I plan on making a offshore bracket to mount the OB on.

    For the Viper, I don't have the HP rating but it was a V6.

    btw, I sent you a photo to your email. Thanks for helping out.
     
  4. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Here is the photo that Ballfeng sent me.
    Re the 'new' rectangular hollow sections shown, is this your proposed way of adding stiffening?

    Ballfeng's transom.jpg
     
  5. ballfeng
    Joined: Mar 2022
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    ballfeng Junior Member

    Yes, the vertical frames will be welded to the original frame on the bottom and to the top lip of the boat frame as well
     
  6. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Well, I don't profess more than a gutcheck.

    Do nothing without the bracket you are using outside.

    Draw it up.

    In general, the rectangular sections are not my favorite. They would be hard to bolt any bracket to if bolting is needed, and they don't really help the transom top as much as an angled knee.

    Be patient and you'll find a great outcome.
     
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  7. bajansailor
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    bajansailor Marine Surveyor

    I shall tag @Ad Hoc and he will hopefully be along at some stage to offer an opinion, as aluminium structures are his forte.

    Some questions :
    How are you planning on filling in the aperture left by the water jet? I think I can see daylight there (?). Will you weld in a filler piece that matches the shape, or weld / rivet on a cover plate, or ???
    Re the blue gunwhale section - is this a box section or maybe an inverted U across the top of the transom?
    Re the two 'extra' blue pieces welded to the underside of the gunwhale, are they (also) box section, or plate flanges?
    Re stiffening the transom for the pod / bracket that will be attached (welded on, or bolted?) I think I would start from the strongest area which must be that substantial keel plate - it looks like the jet intake housing is still there, underneath the horizontal transverse aluminium box section.
    Re the deep channel section that appears to be welded to the transom, between the two vertical box sections, do you want to keep it, or will you be cutting it out? It looks like it was something to do with the old jet assembly?

    For reference, the catamaran in my avatar has 2 x 150 hp O/B motors mounted directly on the transoms, which are 6 mm / 1/4" thick aluminium. The transom top has a 3" square box section welded on to stiffen it, and the transom plate has additional 4" wide plates welded on in way of the engine securing bolts, making the plate thickness 12 mm locally in way of the bolts.
     
  8. ballfeng
    Joined: Mar 2022
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    ballfeng Junior Member

    Interesting points. I drew it up a few times but I'm kind of a hands-on learner so I have to see it in person, hence what I came up with so far. However, since I have that (in the picture) as a foundation, I am thinking of laying the 2x6 by its side up against the transom. I original was just thinking the wider angles would give it a strong structure to begin with.
     
  9. ballfeng
    Joined: Mar 2022
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    Location: CA

    ballfeng Junior Member

    For the Jet opening, Customweld used a plate on the bottom I was able to take it off and I'm going to be welding it shut. For the mount on top, I'm trying to put a frame there since it's pretty solid. However, I didn't want to move forward since I know there are plenty if wiser folks like you all here, to help me (much appreciated).

    Also, thanks for giving me an insight on your setup. Gives me a better picture on what I may need.
     
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  10. fallguy
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    fallguy Senior Member

    Every aluminum outboard boat I have ever been on has a cored transom; usually plywood. What makes you think a few layers of sheet aluminum are gonna be enough?

    How does the bracket attach?

    Never been on any bigger than 20'..
     
  11. ballfeng
    Joined: Mar 2022
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    ballfeng Junior Member

    Oh yes, I was planning to put either wood or weld a rod between the rectangle tubing to keep it from crushing. (got the idea from my BILs aluminum boat).
     
  12. fallguy
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    fallguy Senior Member

    I recommend you clean slate. Give us a picture without any concepts. I think your idea right now is not good and implementation will be too hard. A picture of nothing and people mark it up. Also a picture of the outside and dimensions to the horizontal section would be wise.

    I'll try to stay away from too much comment, but you need to know the bracket and how it attaches before you do anything. In the simplest case, if the bracket bolts on; it certainly can't bolt through at your risers, for example.
     
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  13. Ad Hoc
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    Ad Hoc Naval Architect

    I would avoid mixing aluminium and wood.. not the best of bed fellows unless lots of mitigation!

    Size and weight of O/B and any dwgs of existing structure/transom too?
     
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  14. Howlandwoodworks
    Joined: Sep 2018
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    Howlandwoodworks Member

    CCA lumber has arsenic, chromium, and copper in it. The copper in the treated wood will attack a softer metal.
     
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  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    All good. Here in Minnesota, Lund boats and many other recreational aluminum skiffs are all built with wood cores last I knew. Eventually, they rot. The reason cores are used is outboards are bolted onto 0.065" aluminum and the wood stiffens two cheap layers. It is a classic means of making two cheap aluminum skins strong enough for bolting on ob. I can offer a picture for any doubt.

    I wasn't suggesting to use a core, but attaching a bracket to 0.125" thick aluminum skin seems equally poor. And bolting or welding on a bracket needs to consider the structure/skin. My point was skin might be insufficient.

    OPs layout doesn't seem to address the bracket, or how it is attached.

    Glad you are posting. I'll sit back and learn.

    only for posterity, here is how 99% of aluminum boats have been built here for last 50 years--so bolting doesn't crush the skins..or all stresses concentrate in outside skin, etc.. it is a cheap production method; cap here is missing, of course..this picture is a rot replacement job most likely which affirms your point of course; probably the knees were riveted thru to the outside which makes replacement more fun...

    9E3F4456-89BD-450B-9E4B-FF767E578679.jpeg
     
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