Bolger Fishcat in Aluminum

Discussion in 'Boat Design' started by Pickleman, Mar 11, 2015.

  1. Pickleman
    Joined: Mar 2015
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: NorCal

    Pickleman New Member

    Hello everybody! I've been building homebuilt airplanes for about 16 years now, and I want to try a boat. I live in Northern California, and want to have a boat suitable for calm days out of Trinidad on the ocean and all kinds of days on the Sacramento River, Delta, and the lakes up here. I am not interested in speed, just lazy days fishing with a strong, light, economical boat. I know I can buy one cheaper than building, but where's the fun in that.

    I like the looks of this boat:

    It is small, trailerable, looks stable, and effeicient on light hp. This with a trolling motor plugged on the aft end of one of the hulls could make a nice fishing boat.

    Having built airplanes out of aluminum, fiberglass, and wood and fabric, I must say aluminum appeals to me the most. I have a good assortment of welding tools and skills, and won't be frightened by welding. Given the plywood construction it was designed for, I thought I would proceed as follows:
    Follow plans for number of bulkheads and placement.
    Construct aft bulkheads from welded 3/16 angle and .125 sheet 6061
    Construct all other bulkheads from .125 angle and .090 sheet 6061
    Use .090 6061 for both hulls, drilling and wire stitching the pieces together then welding the seams and filling the holes drilled to wire the boat together.
    Each bottom seam and hull/deck seam would be capped with aluminum angle opened or closed as neccessary to conform to the sides and bottom of the boat. This would also give the boat some abrasion resistance when beached
    Where external stringers are located on the wooden design, I would weld .125 angle in place.

    Any aluminum fabricators out there see a mistake i heading for?
    Last edited: Mar 11, 2015
  2. Kevin Morin
    Joined: May 2013
    Posts: 83
    Likes: 10, Points: 0, Legacy Rep: 72
    Location: Kenai, AK

    Kevin Morin Junior Member

    bolger cat in welded alum.

    I've built boats in welded aluminum before and note a few airplane-like hangovers in your post that might do with some more thinking?

    First- bulkheads in this boat wouldn't need an angle or thickening edges like angle extrusions at the joint to the hull plate, the hull would do that job if even stitched not continuously welded. Bulkheads in welded boats are gain their perimeter stiffness from the hull's skin/plating/panels in welding essentially 90 deg to the bulkhead.

    Next- the idea of using a 60 series sheet materials for the hull skin seems a bit ill-considered as the 50series is much more applicable due to malleability issues and overall welded strength, corrosion and work ability. I suggest moving all the sheet to 5052, 5086 or 5083 depending on what you can buy least expensively in your area? This tiny boat is so small that even the '52 alloy would serve fine as the hull skin.

    Don't bother to stitch and glue the hulls, just cut the developed plates/panels/skins out with a jig saw, clean the edges of burrs and lube, tack together and weld out. Wire is wholly, totally, completely unneeded step.

    Longs inside or outside, if the hull's skin is 0.090", will be challenging so a clamp system that reaches inside and outside to hold- like 24' long 'vise grips'- will be needed to keep the side to the long when they are stitched. This clamp will require a fairly large pad on the feet near the weld zone on the plate's outer side.

    What you evidently can't 'see', at this stage, (?) is that seaming/welding thin aluminum less than 0.125" with a mixture of 0.090" is a 'non-trivial' task compared to welding 0.125" and thicker. I'd say the skill required to do 0.090" hull seams is 10X the skill required to do 0.125" and expect that you already understand that either 0.023" MIG or TIG will be implied?

    As a boat builder of more than a few skiffs, and a half dozen thin skin'd little boats, I'd say it was worth the extra wt, since you're not planning on planing much, to go up to 0.100" or 0.125" 5052 alloy and use a small dia. MIG wire to seam the hull.

    If you were to research the number of new builders that post the idea that they'd build a "small, thin skinned boat to prepare for a larger welded project", then follow up and find 98% of them fail because welding thin is not proportional to welding thick.... I'd say build the boat thicker -it's much easier and easier on the first few boats; seems better to me?

    just my few cents, good luck with the project.

    Kevin Morin
    Kenai, AK
  3. Pickleman
    Joined: Mar 2015
    Posts: 2
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: NorCal

    Pickleman New Member

    Aluminum Bolger Fishcat

    Thank you Kevin, just the kind of advice I'm looking for. Everything marine seems so inexplicable heavy duty to us airplane folks! As for the alloy, I had a bunch of 6061 t6, and have a mig, a square wave tig, and a henrob Dillon torch that can all do the job. I have a few sheets of 5052 in .050 that I bought to make fuel tanks with. I have welded a few up in the .050.
    It seems so soft compared to the 6061, but from my reading, plenty of boats have ben welded from it! So have any NorCal folks got a good place to buy the 5052 in .100?

    And thanks for the note about the stiching. I figured I would use it like I do Clecos on the airframes, but if I can cut out a step, I will. The mig will be fine for skip welding tacks, then go over with the tig.

    Re: the longerons--I have furniture pipe clamps with the reach for those small cat hiuls. I figured using two, one on each side pinching a two by four against the longerons, or the wire stitches. I think I can rig enough jigs and clamps. Would you place them on the outside if possible? Or do you prefer the inside?
    As far as skin thickness goes, I'll be willing to go a reasonable weight penalty for ease, but I've welded enough .050 to know that blowing a hole is just a sneeze or slip of the elbow. I started using the Henrob Dillon and the glasses the tinman -- --sells to flux weld some of the seams on the lighter stuff. Not bad for 54 year old eyes.

    Thanks again for your help!

  4. Dave Gentry
    Joined: May 2010
    Posts: 33
    Likes: 4, Points: 8, Legacy Rep: 50
    Location: Charlottesville, Virginia

    Dave Gentry Junior Member

    Just an FYI - Other than those sold by the late Harold Payson, plans for Bolger boats should be purchased from Phil Bolger & Friends directly. The site you found the Fishcat design on is, under the current ownership, NOT an authorized dealer of Bolger plans, apparently refusing to pay royalties to the designer.

    Contact PB&F here:
    Phil Bolger & Friends, P.O. Box 1209, Gloucester, MA, 01930, Fax: (978) 282-1349
    or on the Bolger yahoo group.

    Fishcat is a neat little boat.

    Dave Gentry
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.