I see they make them - is a plywood/fiberglass outboard bracket sane?

Discussion in 'Fiberglass and Composite Boat Building' started by leaky, Mar 3, 2014.

  1. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    I'm putting a smaller outboard bracket on my 16 foot center console. The purpose is mostly to loose the engine well and cutout.

    It will be minimally-sized to suit the outboard (as small as I can get it so the engine is able to tilt up), which puts the bracket in the 15 inch range.

    Originally I was going to make a non-flotation one out of aluminum, more like a long jack plate, ie big channel cut to the right angle or possible plate and angle bolted together similarly.

    Now looking at what others have done out of fiberglass, I'm wondering if wood and glass would be a better option - I could easily create any shape that way; the weight would probably be similar for such a small object.

    Any thoughts? Anyone know about how thick of plywood and how much laminate this would require to hold a 350 lb ~100 HP engine?

    Jon
     
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hello Jon,

    In the old days we'd get a piece of SS, have a bender bend it in the shape we wanted. If thick enough, that SS is tough, it doesn't rust and it outlives everything on the boat. I'm not saying go for SS. We didn't know how to use fiberglass back then and I once was going to build a boat from fiberglass which turned out disastrous :D I guess we all start somewhere.

    I'm saying you can use anything you want to use, personally I dislike wood.

    If you decide to use fiberglass, just make it thick enough and ditch the wood. You need some kind of former to shape the fiberglass on. You can even create a shape from polystyrene, saw, melt, file cut, sandpaper it to shape and size. Then if you use polyester you have to paint the polystyrene to seal it (use a denser grade) or the polyester will eat it up, water based wall paint is fine. Even if the polystyrene is inside of a shape, you press a hole in it and pour a little petrol in, it will dissolve the poly and you have your hollow shape.

    It is always better to have ribs in shapes to stiffen and strengthen it, you don't ever want to lose a motor...
     
  3. garrybull
    Joined: Nov 2010
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    Location: portsmouth england

    garrybull Senior Member

    ive built quite a few outboard pods in the last couple years for people.

    ive got my own mould to make them.

    it sets the engine back around 28" from the transom.

    lay up is 2 gelcoats and around a 15oz lay up of mat and combi woven.

    plywood is then bonded in to the end of the pod to make it around 40mm thick to bolt the engine to it.

    the pod is fitted to the boat by cutting out a hole in the transom and glassing the pod in place and then the piece that was cut out is trimmed up and fitted back in the transom to close off the hole.

    it can also be bolted in place as well as it has got a 30mm flange all around the edge.

    i have had 200kg sat on the pod and it didn't move at all.

    im just about to design a new pod for my tunnel cat.
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    16 feet is not a size you can go moving a 350 lb weight aft a couple of feet and not notice a big difference. Unless you are aware of it being a success on your model boat, with others doing it. If your boat has a lot of width at the transom, say 175cm chine-to-chine, you can probably get away with it, but if it were 150cm, I'd say forget it. It is entirely different podding a 16 footer to say, a 20 footer, the engine is far bigger percentage of total weight, in the case of the smaller boat. It becomes a different equation if you make the pod a continuation of the bottom, but it doesn't guarantee success. A lot depends on the hull design, not just the pod design. And if the pod is heavy, it just adds to the problem.
     
  5. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    I assume there's gotta be some safe distance I can move it back? When I measured before it appeared I needed 15 inches, so closer to 1 foot.
    That wasn't accounting for the transom angle, the impact of mounting the engine higher for the setback, or the likely possibility of the engine coming partially over the transom at full tilt. All of those things shave some distance off.

    So it's very possible the bracket ends up more like 12 inches or less if I carefully calculate the true clearance required. Do you think even then it's an obviously-unpractical change?

    Another option is I could forseeably find a 25 inch driveshaft & exhaust housing, make the engine I've got a 25 inch (currently a 20) and build the existing transom up to that level. Aside from the work involved in getting the transom extended + modifying the engine, I'm not really keen on that idea though because in the end the engine rigging will all be in the boat. I'd like to put it outside the boat.

    Jon
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    You need to have enough clearance to fully tilt the motor, in the straight-ahead position. That varies somewhat according to what the engine make/size is. That assumes a flat transom ahead of the pod. You could rake it forward without having much effect on the internal space.
     
  7. whitepointer23

    whitepointer23 Previous Member

    this is a ply and epoxy pod I made recently. the boat is a 17 ft Hartley vixen. I have dragged this boat over rough roads, thrashed it in steep chop and it is rock solid, the old Johnson on the back is over 150 kg and the pod handles it fine. I removed a v8 inboard v drive and made the pod to bolt to the old engine beds as well as tabbing it with cloth and epoxy. the pod transom is 2" thick with cloth between ply layers, sides are 1 1/2" thick plus glassed in gussets , no flex anywhere, I am very happy with it. the cav plate is an 1" above the bottom now but I think it needs to go up at least another 1". but even with too much leg in the water I am still getting 33 knots and trimming nicely. the only complaint I have is the pod has made the boat tender with the extra buoyancy. I plan to fix this with an under floor fuel tank. boat transom to pod transom is 400 mm.
     

    Attached Files:

  8. whitepointer23

    whitepointer23 Previous Member

    I would stick with a 20" leg for a pod , the power head will end up pretty high with out the extra 5". you have to remember you are working on a small boat which is more sensitive to these things than a larger boat.
     
  9. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    It doesn't seem you gained much internal space there WP23, what was the object of the exercise for you ? The extra bouyancy of the pod might be handy to keep the powerhead higher, even if the boat has become a little tender.
     
  10. whitepointer23

    whitepointer23 Previous Member

    probably a bit hard to see in the pics mr e, but the pod only extends into the hull about 200 mm so now the inside is flush right across , I don't know the correct word but that is the original capping across the transom which is just deep enough to have a battery each side of the pod. I am going to build a ply box which extends above the pod to mount a bait board on top and tackle trays underneath. when it had the holden v8 the engine box took up 1/2 the cockpit although it was a good seat. the black antifoul gives you an idea of how high the waterline was, now the chines are out of the water.
     
  11. whitepointer23

    whitepointer23 Previous Member

    i only did it this way to utilize the engine beds instead of building a new thicker transom. it works really well so far. i got the boat very cheap and it has no rot otherwise i would not have used a ply hull. so far it owes me about $1200. a lot of boat for that money.
     
  12. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    OK, so the pod is attached to the old inboard engine bed, that sounds like good use of existing structure, if it can take the stresses.
     
  13. whitepointer23

    whitepointer23 Previous Member

    so far so good, it is also epoxy glassed right up each side at transom as well. the transom was 30mm thick from floor level down so the pod is through bolted from the rear as well.
     
  14. leaky
    Joined: Sep 2008
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    Location: nh

    leaky Senior Member

    Hi,

    Thanks for the input guys!

    Some background information though - boat is a 16 foot aluminum starcraft converted to a center console, it has a 20 gallon fuel tank ~1 foot forward from the transom - then 3 batteries forward of that, then a console forward of that. Basically all the weight runs right down center under the deck. Then in front of the console there is about 4 feet, two storage areas there running width-wise - one for fish aft, one for anchor forward. Deck is held up by pressure treated planks, bolted/rivoted to the ribs, bolted to transom, very strong etc.. etc..

    Originally the console was built of 2X4's and 3/4 plywood (top of windshield 6 feet off deck, a "stand up" sort of thing), deck was all 3/4 plywood, there was a livewell of 3/4 plywood forward of the console. Boat had a merc 50 on it. It sat OK in the water (kinda flat) but always felt kinda bow heavy and was slow - with 1 person it could do 30 but with 2 it could barely plane no matter where the second passenger stood. Standing on the transom had little impact to the boat, so I always said just dropping a heavier outboard on the back might fix all of the problems (power and weight distribution).

    I gutted and built the thing 10 years ago when I was broke and in college. Some things I did well, some just couldn't be done so well on my budget. The deck rotted and stuff, was heavier than needed to be etc.. So now what I've done is I'm re-doing the deck with 1/2 plywood and epoxy/glass, console was re-built from angle aluminum and 3/8 inch PVC board sheething, I'm doing it more modern and better while shaving at least 200 lbs of bad weight. I've got a 110 Johnson I overhauled that's going on (admittedly only needed like an 85 HP, but weight would be no different and "free" was the right price for this one).

    With this setup I have alot of freedom to move weight around - for instance the 200 lbs of batteries can go all the way up to the bow if needed.

    The transom I'm closing off by removing the "transom pad" on the outside and I've built one that is larger/higher to completely cover the engine well hole. I can then notch it a bit if I want to allow the engine to come somewhat into the boat without altering the new "closed transom" design a whole lot (ie add a little 1 foot X 2 inch cutout and a sliding door if it makes more sense than moving the engine back a long distance for the same clearance).

    So back to the bracket. My concerns are similar to what Mr. Efficiency expressed; I very much want to go with a bracket but do not want it to cause problems either. Basically I planned to measure the length needed, build no longer than that, then if I want an extra inch I can just add a shim to move it back or change the angle so it can't trim as high (versus being stuck with a bracket that is 2 inches longer than needed) - is this a bad idea?

    Sounds like though there's some difference in opinion on length though. With this type of setup - is there any reason to go longer than required to tilt the engine up?

    Thanks,

    Jon
     

  15. whitepointer23

    whitepointer23 Previous Member

    I prefer to keep pods short as I can, with the v4 you can get away with a fairly short pod, mine is 400mm and it protrudes enough to mount a swim platform each side which I will be doing. you could get away with 400mm if you have a small cutout on the top of the transom to allow for full tilt. I tapered the bottom of mine so it clears the water on the plane and it works well. you must do your home work here because the bottom of the pod will determine how the boat behaves when finished. this is the second pod conversion I have done and it was worth it . good luck.
     
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