A Photo & Discussion Forum for Wharram Design Enthusiasts
someone else in another thread was talking about alloy as a building marteirial, and 10 in alloy tube as beams, they would be very strong and stiff at that size but alloy can fail with repeated flexing where wood is naturally flexible.
The earlier Wharrams flexed a great deal. This made the boats not very rigid. This lack of structural rigidity made for a rig that was unable to hold any headstay tension. This certainly contributed to the lack of windward performance. The newer lashing design allows for a much tighter structure. We tighten our lashings forever more tight. With your hand on the beam and hull together one can feel some movement but it is not visible.
We built two T8m for day charter use in SW florida at the Marco Island Marriott Resort. While these boats do not cross oceans and do not often see big wind or waves, they do go out three times a day 7 days a week for 7 years now. In late 2015 one of the boats was on the hard for maintenance and was struck by lightning. The lightning came down a shroud to the chainplate and blew a hole through the side of the hull,then through the bottom paint to one of the keel blocks (12'x12"x 30"), blowing it apart leaving a basketball sized hole in the concrete. We brought the boat back to the shop or repairs. We thoroughly surveyed the entire boat at that time. The beams showed no signs of wear or degradation.
These beams I designed in house with no engineering other than experience and intuition.They were rectangular in section and were constructed of 1708 and unidirectional fibers over a solid Divinycell foam core. They had extra layers of glass in way of the mast step and where the lashings are located.
When it came to the Ariki 48 I went to Eric Sponberg (naval architect/engineer to help me design the beams. We discussed various building methods and materials. We ended up building female molds for the beams and the beam bottoms. The beams were built hollow with a couple of layers of CSM and 5 layers of 24oz triaxial e-glass. There are internal bulkheads in way of the mast step and lashing points. These beams have so far worked out with no problems.
Building the molds fo these beams cost a lot. For us that is ok because we will use them repeatedly. For a one-off building the beams over a solid foam core would be much more cost effective. I would recommend the use of an engineer to establish cross-sectional area and lay-up schedule.
Beams are a big part of these boats. Wood is maybe the easiest and cheapest route to go but the trade off is weight and longevity. Building beams of aluminum is certainly a viable option. We are more comfortable working in composite.
I've been having to repair small nicks and dings in my wooden beams almost every time I take Beto apart, and it is getting quite annoying! The front beam especially takes a lot of abuse. I know Reinhard Käferböck has aluminum square tubing with no issues, and I think I will eventually crack and go for the same thing. Woods uses aluminum tubing on his Strider design, so I'm sure the 4"x1/8" wall that Reinhard has would be perfectly strong enough for Beto and.......................wait for it...............no maintenance! Having to only worry about maintaining the hulls would make for a much better peace of mind and way less annual yard time, I think. After doing the endless fillets and other bullshit on my wooden beams, I almost wish I had gone with the $500 (for all 3) aluminum tubes instead from the get go.