Both Dominico and Zee have wonderful photos of DUO 900 builds. The hulls do not seem to have limber holes in the bilges or ventilation cutouts in the bulkheads. Is this per plan? I can't imagine a timber boat having a long life without these features even when epoxy coated.

David

Hi David

No holes were not absolutely necessary. If good in the epoxy and the area is closed on a try day, no proplems over a long time periode.

Bernd

Thanks for the answer to my question Bernd.

It has been my experience that limber holes are needed for bilge water to drain to the lowest point in each compartment so it can be easily removed.

I worked as a Shipwright building timber monohulls from 1973 to 1981 and have seen the condition of many of them after all these years. The epoxy/timber boats with good ventilation have had the longest life. Some of them look almost new on the inside after 45-years.

One common problem I have seen on the boats with poor ventilation is mildew on the inside surfaces. The boats with good ventilation did not generally have this problem. The main way we installed adequate ventilation was to ensure each compartment had at least two openings (ventilators or hatches) to the outside of the hull. Lockers and cabinets also need at least 2 openings for adequate airflow to the inside of the hull to stop condensation and mildew. When faced with watertight bulkheads, we installed a low inspection port and a deck ventilator or hatch to induce air flow through the compartment. Both the inspection port and the ventilator would normally be closed when underway to provide watertight integrity.

Over the long life of these boats, epoxy slowly absorbed water. I know this because of the slight discoloration of the timber under the epoxy where bilge water was left. By inducing good ventilation, bilge water evaporates and there is minimal absorbtion of water into the epoxy. Dry wood is stronger and less likely to rot.

Here is a real-life example of the situation. One boat I built in 1977 of cold molded Western Redcedar, okoume plywood and Sitka spruce was sweet smelling with zero rot or mildew until it suddenly began having problems after 27-years. Mildew damaged the inside paint and there were a few small areas of rot in 2 deck beams and a small area of plywood decking. All of these problems were in the forward 1/3 of the hull. The problem developed because the owner closed off the forward cowl ventilator and kept the forward hatch closed tight when moored. The two aft ventilators and companionway vent kept the after portion of the boat in good condition. Closing off all ventilation forward caused the problem. After repairs, the owner keeps the ventilation open forward when moored. 16-years later, he has not had any more problems.

Thank you David for writing detailed about your experience. A lot of stuff to think about.

Gru?, Günter

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Hi David,

Richard, you would be right in an ideal world. My experience is that few "watertight" compartments are truely waterrtight.

I raced International 10 Square Meter canoes and 5o5's for many years. All of them were supposed to have watertight bouyancy tanks. All of them sometimes accumulated water in the buoyancy tanks.

As you pointed out, common problems are from deck leaks. I would add that leaks around fittings and hatches are very common. I always told my customers to plan on re-bedding all the fittings, hatches and so forth every 7 to 10 years as a part of general maintenance. This seemed to prevent most of the leaks. Some fittings that are "bonded" in place per the Gougeon recommendations rarely need re-bedding. So if you have a truely watertight compartment bonding of fittings can help it stay that way. Another help is to provide watertight conduit for wiring that has to pass through the compartment.

Thank you David !

When you write "expoxy-timber", you mean "epoxy impregnated plywood without fiberglass" ?



----- Mail original -----
De: "David Mancebo via groups.io" <mancebodesigns@...>
?: [email protected]
Envoyé: Jeudi 26 Novembre 2020 16:45:20
Objet: Re: [K-Designs-Multihull-Sailboats] DUO 900 Question

Thanks for the answer to my question Bernd.

It has been my experience that limber holes are needed for bilge water to drain to the lowest point in each compartment so it can be easily removed.

I worked as a Shipwright building timber monohulls from 1973 to 1981 and have seen the condition of many of them after all these years. The epoxy/timber boats with good ventilation have had the longest life. Some of them look almost new on the inside after 45-years.

One common problem I have seen on the boats with poor ventilation is mildew on the inside surfaces. The boats with good ventilation did not generally have this problem. The main way we installed adequate ventilation was to ensure each compartment had at least two openings (ventilators or hatches) to the outside of the hull. Lockers and cabinets also need at least 2 openings for adequate airflow to the inside of the hull to stop condensation and mildew. When faced with watertight bulkheads, we installed a low inspection port and a deck ventilator or hatch to induce air flow through the compartment. Both the inspection port and the ventilator would normally be closed when underway to provide watertight integrity.

Over the long life of these boats, epoxy slowly absorbed water. I know this because of the slight discoloration of the timber under the epoxy where bilge water was left. By inducing good ventilation, bilge water evaporates and there is minimal absorbtion of water into the epoxy. Dry wood is stronger and less likely to rot.

Here is a real-life example of the situation. One boat I built in 1977 of cold molded Western Redcedar, okoume plywood and Sitka spruce was sweet smelling with zero rot or mildew until it suddenly began having problems after 27-years. Mildew damaged the inside paint and there were a few small areas of rot in 2 deck beams and a small area of plywood decking. All of these problems were in the forward 1/3 of the hull. The problem developed because the owner closed off the forward cowl ventilator and kept the forward hatch closed tight when moored. The two aft ventilators and companionway vent kept the after portion of the boat in good condition. Closing off all ventilation forward caused the problem. After repairs, the owner keeps the ventilation open forward when moored. 16-years later, he has not had any more problems.

Hi Cyril. I mean timber structure sealed with epoxy. Usually the timber was laminated to make it more stable. So we used plywood, cold molding, and strip planking for hull skins and laminated wood for stems, frames and so forth. Fiberglass would be used to increase puncture resistance of softwoods. If you follow Bernd's plans, you don't need to worry about when to use glass reinforcement. He will tell you when it is needed in the plans.

On our Voyager we ended up with five separate buoyancy compartments in each hull as we divided the bigger aft one into two. We ran conduits through them in some places. Each of the compartments has at least one hole for an Armstrong compression deck plate. (You just need a hole, no screws, and they seal very well, not like other deck plates). The idea is to use computer fans to pull air through the holes when the boat is not in use for a long time. This should allow the sealed compartments to breathe. I hope to avoid metal fittings through the hulls completely. That might be unrealistic, but with “organic” chainplates, cleats and stanchions, we have a good start.?

Patrick