Fibreglass modification & structual Integrity

Discussion in 'Fiberglass and Composite Boat Building' started by firefox7, Mar 12, 2008.

  1. firefox7
    Joined: Mar 2008
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    firefox7 New Member

    Hi all...

    I'm new to this forum and need some valuable advice. About a year ago I bought a boat which is a 5.85 mtr vessel. Formally this was a half cabin boat that had the cabin removed, and converted to a centre console. I do not know the make or manufacter of this boat which I originally thought it was a haines hunter v19 or similar in the haines lineup.

    Anyhow, when they cut the cabin free, they used PVC tubing to make a new border whether it was for structual strength or water run off which runs down the side of the boat and meets up with the original square type border. I have illustrated some pics for you to veiw of what I wish to do to the front of this boat to increase the room available up front. Basically this boat is going to get a full refurbish, paint, new bimini top etc. The idea I want is a semi bowrider up front with the fishing at the rear.

    My question is....the area highlighted in red is the area I would like to remove from the boat. A new border will be constructed to run off the water but i'm concerned about the structual integrity. I don't want it to split up front. Also if anyone has any idea of the make of this boat, please say so.

    Thanking you all.


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  2. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 476, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The HIN found on the transom will ID the manufacture of the boat as will the title in most cases for a modern craft (after 1973).

    PVC pipe has no structural ability, is very difficult to get glue to stick to it (except the welding adhesive used to join other pieces of PVC), it's brittle, plumbing grades don't tolerate UV for very long, it doesn't accept paint well and in general is a Mickey Mouse way of doing things.

    You can remove the remaining deck as you desire, but it would be wise to support what remains to provide some torsional strength to the hull, particularly forward where slamming loads will be quite high.

    Epoxy a bit of plywood under the edge of the new opening. This doesn't need to be very wide or thick, say 1/2" ply, forming a perimeter around the cutout and about 4" deep. This makes a "nailer" to attach a carlin and coming which will channel water away from the opening, plus will stiffen things up a fair amount. Glue and screw a piece 1" x 2" to the under side of this plywood, again following the new cutout area. This is the "carlin" which the coming will be attached to. Now bend in a coming, using 1" x 4" or whatever you intend to make your coming out of, gluing and screwing it to the carlin as you go. The radius doesn't appear to be particularly severe, so you should be able to bend these pieces in reasonably easy. This will leave a seam along the deck edge, where the coming meets the deck. Use a length of quarter round to cover this, bedding it polysulfide (3M 101 for example) and tack it to the coming with finish nails (stainless so they don't rust).

    You're done. If you want it to look nice and nautical, the forward portions of the coming should be taller then the aft areas. Use the eyeball method when bending in the coming pieces, with a slight upward sweep toward the bow. It also looks better if the coming cants outward a little bit. This angle can be incorporated into it by cutting the carlin outer face (where the coming lands on it) with a slight angle (a few degrees will do) on the table saw before mounting.

    Some varnish on your handy work will spruce up the looks of the boat a lot, but paint is easier to care for.

    The drawing should explain things enough. The lower view has the coming canted 3 degrees outboard.
     

    Attached Files:

  3. charmc
    Joined: Jan 2007
    Posts: 2,391
    Likes: 78, Points: 0, Legacy Rep: 840
    Location: FL, USA

    charmc Senior Member

    As usual, PAR has excellent advice. I'd just place a bit more emphasis on the deck reinforcement. Looking at the photos, it appears that the deck molding gave the hull a significant portion of its original rigidity and torsional resistance, i.e. much of its structual strength. Although it will add perhaps 100 lb/50 kg more weight, I recommend 3/4"/19 mm marine ply. Fit it as close as possible to the deck-hull joint (in other words, make it as wide as possible) all around and glass it in as if it were a stringer. Anywhere you encounter deck hardware, like the sampsom post in the bow, remove it and drill to throughbolt after the plywood is glassed in. Overkill? Maybe a bit, but you'll be confident none of the hull's original strength has been compromised.

    For the rest, follow PAR's recommendations. The coaming he describes will do its job and add to the boat's appearance.
     

  4. firefox7
    Joined: Mar 2008
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Australia

    firefox7 New Member

    Thanks for the info guys as it is much appreciated. I have already started to strip the boat. All i have to do now is remove the console and engine from the boat, then the fun part begins. I think I will go a little overkill on the deck reinforcement though, as you have suggested. I have the entire process thought out, and will post up some progress pictures over the next few months. This will be a long project as I intend to take my time and do it right the first time. Besides, fishing season is over in my neck of the woods. Perfect time to do all this.


    Cheers Fellas.
     
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