Strip built cruising cat with xynole sheathing

[Close Call]

Thinking hard about building a 22 foot cruising cat (catboat not multihull). The boat was designed to displace just under 7,000 lbs with 1” strip planking, bulkheads and internal furniture provide the structure not frames or ribs. The boat will be hauled regularly, grounded out on tides, stored on a flatbed and rained on often. I have some hesitations not sheathing the hull and decks with glass or zynole. I also have reservations sealing up 1” planks so they can’t breathe or move. If I was to sheath the exterior would it be in my best interest to sheath the interior as well or just follow good WEST building principals. The boat doesn’t need sheathing for strength I just want to minimize future annual maintenance and upkeep.

I’d really like to hear thoughts from folks who own, maintain or have built medium sized strip built boats. I’ve built, used and repaired a strip canoe before but that is a largely irrelevant experience.

[WI-Tom]

Well, "strip built" is modern epoxy + glass technique, where thin strips (1/4" or less) are covered on both sides with glass, and the glass provides almost all the structural strength.

What you're describing is "strip planking," which uses thicker strips, often edge nailed, and as you point out, does not rely on glass for structural strength.

I built an 18' strip-planked boat and had the same question, and got conflicting advice from credible sources on whether to glass the inside (I did glass the outside). So, I chose not to glass it--less work, less expense, and no certainty. So far, after 4 years, it's been fine. I think I made the right choice, but then again I'm far from an expert.

Tom

[wizbang 13]

An inch thick on a 22 foot boat, multi or any flavor...is very heavy.

[Close Call]

An inch thick on a 22 foot boat, multi or any flavor...is very heavy.

Sure is, the formulas in Elements of Boat Strength point to around 3/4 inch plank stock. I thought of thinning the strips, doing it cold molded or even full blown sheathed strip..........but the plans call for 1 inch and I’m inclined to agree as it’s a heavy cruiser designed to bump bottom while lollygagging along not a race boat.

How thick are the strip planks on a Venus?

[johngsandusky]

I own a 39' strip planked cruising ketch, sawn frames edge nailed and glued, no sheathing. She is tight and sound at 52 years old. On the two occasions that I hauled her for the winter she dried very little and took up in a day or two needing nothing more than her bilge pump. Last winter she was out of water from the first week of October until the first week of June- 8 months.
Good luck, keep us posted.

[gypsie]

Maybe the big planking has to do with supporting the mast.
How will you pull the mast when she's on the truck? It'll be heavy.
If you're going to put her on a flat bed frequently - consider a custom made cradle.
Lots of grounding out - sounds like the boat is in for a rough time. Sheathing might be a good idea.

[Slacko]

As a comparison the strips on my 45 foot yacht are 1" thick, edge nailed, no frames, glassed on the outside only.

[Tonyr]

My strip planked displacenent speed pocket trawler (traditional lobster Boat style) was built 15 years ago to Dave Gerr's sugģested specifications. In my case, that led to 3/4 inch thick Eastern White cedar strips, glued and screwed, overlaid with epoxy and fibreglass. The interior along the keel area was also fibreglassed, the remaining just epoxied.

I bonded 750 pounds of ballast in the bilge to give me a comfortable slow heave in a seaway. The boat is kept on a flat bed trailer in winter.

No structural issues so far.

Tony.

[Close Call]

Thanks Tony, Slacko, Sandusky and Gypsy.

I was studying Gerr last night looking at sheathing options that shows thinner plank stock but outside of heavy glass no options unless you go L. Loyd method. I think I’m going to go whole hog 1 inch or maybe 7/8 with a layer of xynole all around with 2 layers on the bottom. The weight is in a good place down low and it may not be much more than WRC water soakage.......anyone want to hazard a guess?

I have been concerned about mast weight from the start but not structurally, just stepping it. Talked to forte spars, I think I’m going to go carbon, at 40lbs it’s less than half the weight of what I can build from easily available materials. If I wasn’t going to step it more than once a year or owned a crane I would build it per plans, spruce with four staves. Carbon at 40 lbs means a really simple A frame mounted to stanchion bases should make quick work of it.

In case if anyone is interested the cat I’m looking to build is P. Bolger’s leeboard catboat. Flat bottomed with radiused chines and yes with leeboards. See “Boats with an Open Mind”

Keep the real word experiences coming. I’m not lofting till the snow flies.

[Close Call]

My strip planked displacenent speed pocket trawler (traditional lobster Boat style) was built 15 years ago to Dave Gerr's sugģested specifications. In my case, that led to 3/4 inch thick Eastern White cedar strips, glued and screwed, overlaid with epoxy and fibreglass. The interior along the keel area was also fibreglassed, the remaining just epoxied.

I bonded 750 pounds of ballast in the bilge to give me a comfortable slow heave in a seaway. The boat is kept on a flat bed trailer in winter.

No structural issues so far.

Tony.

Tony-

Does your boat have “floors” of some kind? What was the laminate schedule used outside and in the bilge?

The cat is seriously stout but if I’m going to sheath it, I’m of the opinion it needs to be bomber on the outside

Thanks,
Jason

[Jay Greer]

I remember when we built the L36 sloops at Chapman Boat works in Costa Mesa CA that the bronze ring shank edge nails (known as anchor fast nails) and casine glue held them together very well, so much so that many of them are still sailing. One edge of the 7/8" thick planking was coved and the other was bull nosed to allow the planking to conform to the molds. No framing was used except the ring frames at the mast step and running back stay attachments. This was at the beginning of the trend towards monoque hull construction and it worked very well! The hulls were sheathed in fiberglass which was also in its beginning as a marine construction material. All in all it worked very well and produced a strong lightweight hull that was and is a bitch to repair if the planking is ever damaged!
Jay

[Flobart]

. All in all it worked very well and produced a strong lightweight hull that was and is a bitch to repair if the planking is ever damaged!
Jay

There is a book by Hub Miler "The Laminated Wood Boatbuilder", there is a section devoted entirely to the repair of cold moulded and strip planked boats. It may be worth seeking out if you believe repairs to be difficult.

[wizbang 13]

It is a myth that strip plank is difficult to repar.
It is not done with ultra sharp chisels, wood body hand planes,japanese saws or yankee screwdriver.
it is done with a sawzall and a grinder.
easy peasy