Rub rail options for plywood cat

Discussion in 'Boat Design' started by xellz, Nov 24, 2019.

  1. xellz
    Joined: Jul 2017
    Posts: 106
    Likes: 4, Points: 18
    Location: Japan

    xellz Senior Member

    I'm about to start to work on 30ft cat designed by Richard Woods. Current docking situations looks like this. Photo attached. Tide variation is more than 2.5m, ropes are fairly long and with strong winds sometimes there is quite a bit of impact from the fenders.

    I've been thinking of gluing timber strip after hull fiberglass sheathing. Then add something like 4-5 layers of 300gsm glass, maybe more. The idea here is to help spread impact from fenders, add something robust, stiff and hard for fenders locations. I want to avoid any extra holes/fastenings through plywood as much as possible.

    Richards also agrees that it's better to have rub rails in my case. Anyone has knowledge on this topic? Which rub rail solutions could work on plywood hull?
     

    Attached Files:

  2. Blueknarr
    Joined: Aug 2017
    Posts: 707
    Likes: 115, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    I once employed "rub boards". Tw/o parallel twelve foot long 1x6 with fenders attached continually on boat side. I didn't feel the need to protect the pilings. Spread the blows quite well.
     
  3. baeckmo
    Joined: Jun 2009
    Posts: 1,118
    Likes: 117, Points: 63, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Take a look at the local fishermen's solutions; they know what works!
     
  4. fallguy
    Joined: Dec 2016
    Posts: 2,171
    Likes: 144, Points: 63, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I purchased a commercial version that is used on Lagoon cats.

    It cost about 1k per hull...pretty, but pretty spendy...shipping inside the US was $450 to my door due to the length...ship cost would kill the Japan idea; nearly killed it for me

    I strongly considered wood, but wanted the aesthetics.

    I am also using 316 strakes where the cleats are. Those are 14-18" long; shorter if a space issue..

    For a wooden rubrail, I would use hardwood; not pine. I would make is about 2" wide by 3/4" thick and then radius each side with a roundover bit. Apply after sheathing the boat with fillets both sides and then a piece of 6 oz woven tape if you can find one 6-8" wide; otherwise cut our own. The tape is just to encapsulate.

    If you want to pretty it up with steel; you could easily apply a stainless strip up the middle later.
     
  5. philSweet
    Joined: May 2008
    Posts: 2,234
    Likes: 140, Points: 63, Legacy Rep: 1082
    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    I'm with Blueknarr, fenderboards are the way to go, and have countless other uses. Hang fenders at bulkheads and hang fenderboards outboard the fenders. Loads get put to the hull at the bulkheads. 2 x 12's work as gangplanks and bulletproof bulwarks for lashing sails and the jug farm when at sea.
     
  6. Blueknarr
    Joined: Aug 2017
    Posts: 707
    Likes: 115, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    With all respect to Fallguy, I wouldn't glass over rub rails. I would let them be semi sacrificial.

    Is a stand off anchor possible?
    Is hooping the pylon possible?
     
  7. xellz
    Joined: Jul 2017
    Posts: 106
    Likes: 4, Points: 18
    Location: Japan

    xellz Senior Member

    The boat from left side in photo is my current mono with inboard diesel. That's where cat will be tied too. Concrete wall, nothing else is there. Listening to local fishermen was a bad idea that cost me quite a bit. But in the end, was my fault that i listened and didn't learn in more detail myself. Plywood large boats are really rare in Japan, mostly limited to sailing yachts and build from birch ply, not okoume.

    Nice suggestion with fender boards, first time i see this method mentioned. This sure is good for here, especially will help to reduce fender wearing off quickly on rough concrete. I just need to figure out best way so it won't get too much in the way of using boat.

    I thought about adding permanent anchor/mooring point to pull the boat away from wall a bit during strong wind days. But not sure how to accomplish this. So for now rely on ropes and fenders only. I also don't want to mess too much with ropes that are staying in water, it's just way too messy. Brown slime quickly accumulates on them and is a pain to wash off. On the positive point, due to this brown water there is basically no marine growth on hulls, so a hard smooth bottom paint and need only a light power wash once in a while.

    What about my initial idea? I.e. use softwood board as kind of core material and build up thick layer of glass over it? Since it's just one strip each side, additional weight should be negligible. Don't think it will wear off quickly with fenders/fender boards. Just repaint/glass repair when needed. Hardwood would be better to bolt to hull without any glass, but i don't think this method is good on plywood hull.

    And just to know which boat we're talking about - Sailing Catamarans - Jazz 30 fishing, day charter or cruising https://www.sailingcatamarans.com/index.php/designs-2/6-powercats/438-jazz-30-fishing-power-catamaran
    Cardboard model in there is mine and shows more or less end shape i'm going for. Quick work just to get the feel for size and to help me understand plans better.
     
  8. fallguy
    Joined: Dec 2016
    Posts: 2,171
    Likes: 144, Points: 63, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I am just light glassing to reduce ingress. The other option is sticking them on with 4200 and bolting them for a more throwaway option.

    But the bigger issue is they probably won't even hit the dock if it is too low, so you need to go measure things there.

    The rubrails go on the outermost vertical chine.

    If the wharf or pier is lower; fenders will be doing the job or the fender board.

    what about mooring whips?
     

  9. fallguy
    Joined: Dec 2016
    Posts: 2,171
    Likes: 144, Points: 63, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Here is BH2 in cross section of the sister Skoota 32. The rubrail belongs at the black arrow and may not even touch the dock.

    Just so you know I cleated on top and I added rub strakes at the red arrow below cleat locations (well, the strakes fit on the edges actually.. 281DFB73-1D1D-42C0-8648-9B0CB1B1FFDB.jpeg
     
Loading...
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.