Cedar Stringer?

Discussion in 'Materials' started by Skua, Sep 5, 2013.

  1. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    I have a section where my stringers drop down from 2x8 to 2x2 in the last 4 feet of the hull to the transom. The transom needs to be replaced and is on the list of things being done now. The 2x2 section is rotted, I have a pair of 2x8 roughcut, 100 plus year old cedar planks that I would like to use. I seee conflicting opinions on cedar. The idea is to remove the rotted whatever, and place the cedar planks into the fibeglass channels, then laminate epoxy and fibeglass over the exposed area, down over the exist fibeglass. Good idea??
     
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 122, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Fine idea as long as the cedar is sealed in epoxy first all sides three coats and as long as the wood scantlings are based on a similar strength core. If the original wood was white oak, for example, it would be wise to beef up the cedar to a somewhat larger section. Might as well do the whole job in epoxy to increase the longevity of the job.
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Epoxy over 2x stock isn't a good idea, particularly with woods that are prone to checking and as much movement as cedar. If you want to use the cedar, rip it down to 1x8's and laminate them together, making a 2x8. It would be wise to flip one of the halves so the grain alternates as well. Internal stresses inside the cedar are greatly reduced in this method and you have a glue line that can prevent moisture from getting at half of the laminate if there's a coating breach down the road too.

    Can you provide a picture of the stringer arrangement, as the 2x8 reducing down to 2x2 at the transom doesn't sound right. A typical setup would have the 2x8's continuous height from transom forward, with the bottoms curled up, as the deadrise eats into them, in the forward sections of the boat.
     
  4. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    I will post pics soon.
     
  5. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 122, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    PAR, I understood that only 2x2s were being replaced, not wide planks. I agree that pieces such as 2x8s would be too wide to bond in. I do think 2x2s are okay in this case. Cedar would also work unless as I said if the design didn't require a stronger wood for whatever reason.
    Cedar, in other words, should be fine in the case of 2x2s if cedar is used at all. certainly well enough to outlast the rest of the boat.
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Okay, I must have misunderstood the question and description, which isn't unusual for me (just ask her). I'll wait until the pictures come in as I still have a problem with the mental image I have of these stringers, shrinking down from 2x8's to 2x2's at the transom.
     
  7. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    Boat is an '86 Bayliner Contessa, ( yes a Bayliner) flybridge cabin cruiser 28 ft long with 10ft beam. Used for weekend overnighting and week vacations. Power is from a single Chevrolet 5.7 coupled to a Volvo Penta AQ280. Current cruise is 22-25kts and flatout is 32kts at 4800 Manufacturer say weight is about 6500 lbs, but others having scaled theirs loaded out say closer to 9000.

    First pic is of interior before the chainsaw came out.

    Gas tank started leaking and was the catalyst for a large scale project that has been put off due to using the boat. Bulkhead seen in second pic is the cabin bulkhead, that sort off seperated the cabin, engine, and fuel tank bilge compartments. Area that is cutaway, originaly only came 6 inches lower where a series of motley odds and ends "supported" the flooring over the fuel tank. The fuel tank stuck back another 7 inches into the engine compartment, and had a cofferdam, that trapped water, and eventually fuel, resulting in the rotted engine supports seen in this pic. Also the transom is partially rotted and is on the list while we're here. Cofferdam has been cutaway already.

    The next pics show the main stringers 2x8, where they are cutdown and notched for the bulkhead, floor, cofferdam interface. After that you can clearly see where they are now 2x2. The 2x2 pressure treated stanchions epoxied on top were added by me, to temporarily support the rear deck until this project was under taken. Due to the poor rear bulkhead design, and water leakage therefore, the deck had some bounce in it. This is also the main reason for the tank leak. Also gelcoat has lots of spider crack where the gunnels meet the cabin bulkhead, due to flexing, I believe, caused by, stringer and bulkhead arrangement.

    The outer stringers are 1x8 and run to the transom. All the stringers are sectional and are butted to plywood "bulkheads", and supports. No scarfs. Seems to have held up for 27 years that way.

    After tank was removed, the cause of a hull soft and flexible spot became apparent. The bilge deck had rotted under the tank, but, where as most of the hull appears to be 4-6 layers of roven and resin, here, only half of that went on the hull and half was used to ,poorly, cover the bilge deck which rotted. So under the tank the hull is half as thick as everywhere else.

    All of the interior "furniture" was ply and resin, and was cut away and trashed. Intent is to lower the cabin deck 3 inches, and install new furnishings.

    Main plan is to

    1 replace gas tank, water tank, and holding tanks, replace bilge deck and make the cabin rear bulkhead a solid structure down to the hull instead of a truss over the fueltank. Replace cabin deck.
    Materials will be ply and epoxy.

    2 repair engine supports, and stringers, and possiblely add another stringer/keelson, on the centerline, from mid cabin, where one from the bow stops, to part way under the engine.
    Materials for engine supports, will be 3M, Nida Core. I intend to leave engine in place, grind out rotted wood, and fill cavities with N/C.
    Materials for stringers will be Cedar? White Oak, Or what appears to be a hard Pine , Plywood is also a possiblity, and epoxy and FG. I posses all of this, in appropriate sizes.

    3 replace transom
    Materials will be Marine ply, Epoxy and FG, in alternating layers varying from 1 in at the top to 2.5 at the bottom, following original pattern. Holes for attachments will be taper bored and solid epoxy plugged and redrilled for a waterproof seal.

    4 redesign Cabin interior, and install ribs to help support, gunnel to window, to flybridge, structure.
    Materials and design, TBD

    I am open to any ideas or constructive critisms, and would gladly welcom ideas for the interior redesign.
     

    Attached Files:

  8. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    Is 1808 Biax, sufficient for adding back the missing laminate thickness or would some 24oz roving be more appropriate. I have plenty of the 1808 available, but nothing else at moment.
     
  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    1808 will do much better than roving, using epoxy, though having the mat stitched to it will suck up resin like crazy, lowering the fiber/resin ratio (not good) and weakening the laminate (mat has little strength). As a rule, you don't need mat in an epoxy laminate. It's a bulking agent, necessary in polyester laminates, but not epoxy.

    24 ounce roving is strong, but not as strong as two layers of 12 ounce cloth or 3 layers of 8 ounce cloth. Yes, it saves time, but is weaker and harder to work with.
     
  10. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    I will see if I can remove the mat. I picked up a lot of ST Gobain 4in tape and 50 in rolls for 49cents and $2.50 per yd, respectively.
     
  11. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you can't, (it's a pain in the ***), just accept the increased resin requirements and try to roll it out good, to get the best resin/fiber ratio you can. Bag it where practical, if you have this option.
     
  12. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    Thank you. What do you think of the stringer step down, and my plan to size back up? Evidence seems to indicate this as a weak spot as indicated by the spider cracks. I have decided I might laminate a pair of 1x8 oaks together, instead of the cedar. The cedar needs to be ripped down to dimension anyway, as it is rough cut and too thick to start. Just wanted to use what I had.
     
  13. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 487, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yep, that sounds like a good approach and would be what I'd do. I'll add increasing tabbing generally in the area will help too. If you use a red oak, then soak it in epoxy, not just coat it. Red oak is the weak kneed sister to white oak and it absorbs moisture just at the mere mentioning of water. You can use reds, but my routine is to get it saturated. I use the "hot on hot" method, but soaking will do too.
     

  14. Skua
    Joined: Apr 2013
    Posts: 147
    Likes: 5, Points: 18, Legacy Rep: 73
    Location: Hunt's Pier WW NJ

    Skua Senior Member

    I have several board feet of white oak 1x8 so that'x what I'll use. Now I need to find a use for the cedar. Thanks for your input!
     
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.