Narai MKIV Without Beam Troughs

[Budget Boater]

Because I have come to very much dislike beam troughs, I plan to eliminate them and mount the beams on the deck in a fashion similar to the Tiki 30.

Beam troughs are a maintenance item. The area is put through some serious loads that usually cause cracks over time. I have personally seen multiple Wharrams with rot in/around the beam troughs. They are also a pain to build and align, and are cumbersome to work with.

The original MK I had the beams mounted on the deck as did several other early classic designs. I think that the later MKIV designs left the beams in troughs for visual appeal more than for structural concerns. Having owned a Tiki 30 with deck-mounted beams and seen countless other Wharrams with deck-mounted beams, I am not adverse to them (especially if they save me building time and long-term maintenance.) Another aspect will be the physical deck boards will either be mounted to the lower edge of the beam troughs (most likely), which will necessitate one stepping over the beams when moving fore and aft, or mounting the deck boards flush with the tops of the beams, which will necessitate one drop down into the center hull area like a modern Hunter monohull.

The real trick will be reinforcement of the deck at the beam locations. For this, I will combine normal reinforcements of the beam troughs, under-deck triangular Tiki 30 style reinforcements, as well as an under-deck reinforcing plate on both the hull's sides and decks.

Wharram has three basic types of beam mounts: Classic type, Tiki lashing, and web strap (Tiki 30.) Having seen all three in action, I am most definitely a fan of the web strap, and I plan to use a modified version of this. There are some important factors to consider for any beam attachment: strength of the fasteners and slippage. The first one is self-explanatory. The bolts used in the classic type mounting system have a working load of ± 3500lbs, and a breaking strength of approximately 17,000lbs. The 4" wide straps I intend to use have a working load of 6,600 lbs (the ratchets are even stronger) and a breaking strength of 24,000 lbs. These straps will be physically attached to the hull/deck to provide the utmost in strength.

The second factor refers to the ability of the beam and hull to slip apart (athwardship) under strain. Wharram usually solves this problem by bolting the beams to the hull/deck in some manner. However on the Tiki 30 he uses hardwood location blocks that do not allow the beams to move side-to-side under load provided the straps are tight enough to keep the blocks in their deck stops/chocks. This will be the method I intend to use.