Risk of wood rot on a well maintained boat?

[mariobrothers88]

Hi guys I am looking to build a 35' catamaran (either one of woods or waller) using either plywood/epoxy or foam core. Since I have experience with plywood and epoxy and zero experience with foam core, I would like to go with plywood and epoxy but the thought of wood rot makes me nervous. What are the chances of wood rot on a well maintained and properly sealed boat? Is it like less than 1% and essentially trivial or higher risk than that?

What are the things you have to do to maintain a plywood/epoxy boat to ensure no wood rot other than not crashing your boat? How often should you be inspecting the boat and what things should you be looking for?

 

[bajansailor]

What are the chances of wood rot on a well maintained and properly sealed boat?

I would say very slight.
Especially so if you use good quality marine plywood.
Look at the many Peter Spronk designed catamarans in existence - many were built in the 70's and 80's using high quality Dutch Bruynzeel marine plywood and they are invariably still immaculate (there are a couple of them here in Barbados, engaged in the day charter trade).
Some have probably had repairs required, but fibreglass boats would probably also need repairs if they were in the same situation at the time.
The Spronk cats often have the interior hull structure clear coated / varnished over the epoxy - one advantage of this is that you can see much more quickly if there are any small patches of rot developing.
In the same fashion as a balsa cored deck on a fibreglass boat, when you are installing deck fittings on a plywood deck you could drill the holes over size and fill them with epoxy resin before drilling again to suit the diameter of the fastening - this way the plywood is sealed if water manages to get underneath the fitting, and seep down into the bolt holes.

Which Woods design are you thinking of building?
Although the link below says 'over 40', these boats are over 30' length.
Sailing Catamarans - First Choose a Design http://sailingcatamarans.com/index.php/designs-2/5-catamarans-over-40ft

And similarly the Waller design - I am guessing probably this one?
Mike Waller Yacht Design - Coral Sea 35 Catamaran http://www.wallerdesign.com.au/cs35.html
Or maybe this one?
Mike Waller Yacht Design - W1100 Catamaran http://www.wallerdesign.com.au/wal1100.html

 

[sdowney717]

Using foam core a future buyer would prefer that. To most people if they have wood in the hull structure they are considered wood boats. And wood boats have a well deserved bad reputation for rot don't they.

 

[fallguy]

I am building a Wood's boat in foam. It is a LOT more work than a plywood hull. A LOT like as in multiples in time budgets.

There are a few things to be super vigilant about building in ply.

1. All through hull penetrations need to be overbored, refilled with thickened epoxy and rebored for final fastenings and then you use the butyl or 5200 or 4200 inside the epoxy lined hole. This way, should a fastener leak; it only leaks down through and not into the ply veneers.

2. No ply veneers can be exposed. Easier said than done, but all veneers edges must be glassed and glassed well enough to not leak.

3. Xtra insurance is obtained by sealcoating the ply insides with epoxy. Use 2 oz per yard.

4. Be religious about the other 3.

Richard will also probably give you glass minimums that are required to reduce ingress. For example, a 12 oz biax tape is far less likely to leak water than 6 oz woven.

Inspection holes or pie eyes in water tights.

Gutter all horizontal hatches and drain the gutters to thru hulls.

 

[Will Gilmore]

Bajansailor is right, the chances are small, if the wood is sealed and attention is paid to areas of hull penetration. A properly laid glass over wood hull doesn't separate glass from wood. It is also very easily repaired in any port. I grew up aboard a glass over plywood boat in the 70s and she is still being chartered out of Clearwater Fl. today. Same is true of my father's even older 65' fishing boats, built in the 60s.

-Will (Dragonfly)

 

[sdowney717]

Bajansailor is right, the chances are small, if the wood is sealed and attention is paid to areas of hull penetration. A properly laid glass over wood hull doesn't separate glass from wood. It is also very easily repaired in any port. I grew up aboard a glass over plywood boat in the 70s and she is still being chartered out of Clearwater Fl. today. Same is true of my father's even older 65' fishing boats, built in the 60s.

-Will (Dragonfly)

Are you talking glass over plywood on new construction? I can believe that. I dont believe you can glass over carvel planking on an older boat and expect it to last like your examples.

 

[Will Gilmore]

Yes, news construction.

-Will (Dragonfly)

 

[bajansailor]

Are you talking glass over plywood on new construction? I can believe that. I dont believe you can glass over carvel planking on an older boat and expect it to last like your examples.

Curlew is a Falmouth Quay Punt, originally built in the late 1800's - many years later she was fitted with a cold moulded outer skin of kauri timber and epoxy in New Zealand.
Curlew http://classicyachtinfo.com/yachts/curlew-2/

Here is a nice article about her.
https://www.washingtonpost.com/archive/sports/1999/04/13/around-the-world-without-leaving-home

And a couple of nice articles about their life in South Georgia -
Friends of South Georgia | People http://www.fosgi.org/about-south-georgia/people/

August 2008: TIM AND PAULINE CARR - REFLECTIONS ON KING EDWARD COVE - South Georgia Museum http://sgmuseum.gs/news/august-2008/

Curlew is now on display in her home town at the National Maritime Museum in Falmouth.
Falmouth Quay punt "Curlew" – BC09 | National Maritime Museum Cornwall https://nmmc.co.uk/object/boats/falmouth-quay-punt-curlew/

I remember seeing Curlew at Antigua Sailing Week in 1987 - this was before the Antigua Classics Regatta had started, so they raced against the die hard race boats of the day on equal terms.
And much to the chagrin of the race boats, they beat many on elapsed time, and then beat them even more on corrected time - I think she won her class against mostly IOR type race boats - not bad for a 100+ year old wooden gaffer.

 

[fallguy]

Another place where people screw up with plywood is dealing with exposed end grains; they incorrectly assume epoxy neat coats are sufficient.

In building a transom, for an easy example, the transom edges are rounded and then glass overlays are done and then you can square the edges back with simple jig molds covered with shipping tape.

If you want square edges; do not make the mistake of trusting the open veneer to avoid fairing the tapes or glass seaming.

Always round the edges, then glass, then fill back to desired appearance.

I used 3/4" ply in literally two places in my build.

one was a benchtop woth a locker under

I put one hull outside for space reasons and failed to put a drain in that locker and it filled to the top woth water; despite an epoxy sealcoat, water saturated the marine plywood top; the wood swelled; a glass seam split and my fairing got messed up and you can literally see the wood grain in the paint--so, wet bilges, for example, must be glassed all around; had I glassed the back of that panel; pretty unlikely would have had any issue, but the fact I allowed water in there and no drain was really malfeasance on my part

 

[sdowney717]

When I replaced my transom on my EggHarbor carvel boat, I did not build it back the way OEM had done. They used 1/2 inch plywood on a fancy contoured frame of oak that may have been independent of the planking as its own structure, and covered over that with 1/2 inch Mahogany. Needless to say, it was all pretty rotten...
I simply created a new frame work that was dependent on the outer planking, and doubled up the upright posts, but it is all basically independent parts, and is all PT SYP. My independant parts were also more than twice the original dimensions of the original framing, and I cut and ground them to fit the shape of the outer planking hull. After that was done, I planked over it using 1" Mahogany planks of random widths, but all planks were at least 6 inch in width. I bent them around around the curved transom using a comealong and ropes attached to the boat stands and screwed together with SS square drive deck screws 3 inches long. So its strength relies not just on itself, but also the whole exterior of the boat hull. It has been 20 years now and is still in perfect shape. For the section below the swim platform, I used SYP PT deck boards, since no one can see them, there was no need for mahogany down there. It was caulked with PL premium and sawdust mix, in every seam, and just paint, then in 2006, I coated it with Sani Tred Permaflex polyurethane and at my 2014 haulout, I overcoated the wood with the Black PL roof and flashing polyurethane, mostly as an experiment.

Here is a bottom view in 2014 and the other is when I restained with Thompson Acorn Brown transparent deck coating. I cleaned off the gold lettering after it dried with a solvent.

 

[sdowney717]

If you dont add the milled fibers to the black PL, guess what eventually happen with scraping off barnacles in the water. it eventually rips up the coating. My bottom paint has worn out about 2 years ago, and I get in and scrape and it really is hard on the coating. But places where I mixed in 30% milled fg fibers into the black PL, it is holding up, those fibers made a tougher coating. It would also be easy enough to use the black PL and fiberglass cloth. But being a wood planked boat, I dont know if when the wood swells a little what that might do. Probably you need a fabric that can stretch without breaking its strands. Just mix in with a wide blade putty knife, then use that to spread it like frosting a cake onto the hull

 

[mariobrothers88]

Thank you for the response fallguy, I really appreciate it!

Do you recommend I use a round over router bit on my router to do the rounding? What is the rationale of why you need to round over the edges of the plywood, and why aren't epoxy neat coats sufficient? By the way, what do you mean by "neat" coat? Like a single layer of epoxy done neatly? Forgive my ignorance!

Also, would I need to do this for every piece of plywood that I use, even on the hull and bulkheads? Or just the transom?

Thanks again for your advice I really appreciate it!!

Another place where people screw up with plywood is dealing with exposed end grains; they incorrectly assume epoxy neat coats are sufficient.

In building a transom, for an easy example, the transom edges are rounded and then glass overlays are done and then you can square the edges back with simple jig molds covered with shipping tape.

If you want square edges; do not make the mistake of trusting the open veneer to avoid fairing the tapes or glass seaming.

Always round the edges, then glass, then fill back to desired appearance.

I used 3/4" ply in literally two places in my build.

one was a benchtop woth a locker under

I put one hull outside for space reasons and failed to put a drain in that locker and it filled to the top woth water; despite an epoxy sealcoat, water saturated the marine plywood top; the wood swelled; a glass seam split and my fairing got messed up and you can literally see the wood grain in the paint--so, wet bilges, for example, must be glassed all around; had I glassed the back of that panel; pretty unlikely would have had any issue, but the fact I allowed water in there and no drain was really malfeasance on my part

 

[mariobrothers88]

Also what do you mean by "sealcoating the ply insides with epoxy"? How would you go about sealcoating the ply insides?

Thanks again for all your help!!

I am building a Wood's boat in foam. It is a LOT more work than a plywood hull. A LOT like as in multiples in time budgets.

There are a few things to be super vigilant about building in ply.

1. All through hull penetrations need to be overbored, refilled with thickened epoxy and rebored for final fastenings and then you use the butyl or 5200 or 4200 inside the epoxy lined hole. This way, should a fastener leak; it only leaks down through and not into the ply veneers.

2. No ply veneers can be exposed. Easier said than done, but all veneers edges must be glassed and glassed well enough to not leak.

3. Xtra insurance is obtained by sealcoating the ply insides with epoxy. Use 2 oz per yard.

4. Be religious about the other 3.

Richard will also probably give you glass minimums that are required to reduce ingress. For example, a 12 oz biax tape is far less likely to leak water than 6 oz woven.

Inspection holes or pie eyes in water tights.

Gutter all horizontal hatches and drain the gutters to thru hulls.

 

[fallguy]

I am a member of the boat builder central forum. It is the experience of builders on the forum that simple epoxy coatings are insufficient to seal things like transom tops. The reason is very simple. The sun hits the transom edges and the paint, epoxy, glue, and wood have enough cte variation that it inevitably always opens up.

Yes, a roundover bit is best with a bearing. Run it at about 3/8" or jist shy of that.

Here is a picture of a jig on an upside down foam hull. The jig allowed for easier fairing back to square to make the transom look more professional. In this case, the sides and bottom were all squared off. A transom in powercraft requires a square bottom edge for a clean exit and reduced drag as well.

A sealcoat is a neat coat of epoxy in the bilge. In ply on frame construction, anytime you have a chance for a wet bilge; sealing up seams and encapsulating the plywood will give you a longer boat life. Unlike the transom top, the bilge is not affected by sun so much. And if you are not glassing, then a coat of epoxy is wise for certain hulls. 2oz per yard is the rate I use for neat coats

Also, rounding the plywood is done so you can lay glass over the transom top edge. Anywhere you want to glass cannot have a sharp edge. Always must use rounded edges. Return those to square on as needed basis. Transom bottom is 100% required to be square on powered vessels to reduce drag.

 

[fallguy]

The only time glassing is required is if endgrains are exposed to the heat of the sun or water.