|Composite KITSET 10m TRIMARAN
DESIGNED BY ANGELO LAVRANOS
The “doyen” of multihull design, Dick Newick, once said of multihulls, pick any two out of three, Speed, Comfort, Low Cost. Actually these are the basic perameters that need to be “traded off” against each other to arrive at the correct “mix’ for the intended uses of the boat.
In monohull terms you can be a John Spencer (or Dick Newick) “purist” but comfort and cruising utility is then the “discard”.
This trimaran is similar in aim to my ply “Proteus” Cat design.
She is intended to be a fast cruiser for local sailing and also capable of coastal passage making. She will be fast enough in club racing, to be categorised quite a fast multihull, even if a bit slower than new dedicated racers. She will leave older multihulls in this category for dead, since she has modern beam (righting moments) and a powerful rig to match.
She is also very light for a 10m “offshore” boat. Although the EU recreational Craft directive puts her firmly in the Category B (coastal 4m significant wave ht F8 beaufort) by the“multihull size factor” safety criterion, I see this boat (if there is no regulatory impediment and is Cat A equipped) is capable (adventurous) hands at least two up in summer to do longer passages, in the same spirit as slightly riskier small boat voyager’s of the past.
When all is said & done she is still well over 3 tonnes loaded, hugely stable when reefed and a very capable 10m LOA. She uses a prelaminated CNC cut kitset (10 panels) of glass/PVC foam/epoxy sandwich panels which would be set in a 7 station CNC cut female MDF jig and the joints epoxy taped. There is very little external (or even internal) finishing.
The whole boat is absolute minimum labour throughout to build. The kit is designed for perfect easy fitting with simple curvature. Many kits on offer have compound curvature are hard to fit, are not repeatably accurate, and often require forcing or kerfing the panels.
The kit is for a 9m x 2m cutting bed (SP Gurit in Auckland accommodate this size). She is intended to be “demountable” so that the crossbeams, hull, outriggers (amas) can be easily dis-assembled for transport. It is not (at this stage) intended that the outriggers may be hinged or pivoted to reduce beam in a marina.
She is designed with 200% buoyancy floats, with buoyancy well forward (to avoid stuffing/pitchpoling), slightly immersed (to reduce waveslap at rest) and good waterplane characteristics for load carrying. Initial budgeting runs to about $120,000 NZD for the kit, rig, main+jib, and basic equipment, excluding assembly. Kevin Johnson boatbuilders in Devonport offer professional assembly to various stages. The boat is designed for an outboard motor mounted on the transom.
A single cylinder saildrive diesel is an option. Tiller steering, a folding dodger may be fitted over the companionway hatch at the fwd end of the cockpit. The rudder is “kick up” and the daggerboard board in entirely inside the hull when up.
Traditionally minimalist low budget home build boats utilise plywood as the material of choice. However now that “spare time” is either non existent, or “as valuable” as spending cash, the labour content has to be factored in.
The plain truth is that (even a kitset) ply boat has many hundreds more hours of labour than using composite panels in exchange for increased cost initial cost. In the case of plywood hundreds of scarph joints have to be planed, fitted & glued, since the original sheet sizes are only 2.44m x 1.22m. On the composite boat there is very little joining since the big parts are 9m long, and the “H” joint used is an easier and more reliable joint to make.
The composite boat panels are stiffer and have far fewer supporting internal parts and no longitudinal parts to fit internally, and the building (female) jig is far simpler. The ply boat has dozens of stringers & small webs, and has to be externally sheathed and needs far more bog & fairing, & external strapping, while the composite boat does not need sheathing or external strapping so the boat also remains essentially “fair”. The composite panel edges consist of a thin “edge” where the core is chamfered away 50mm from the edge and the inner skin is lapped with the outer.
The edge has a very shallow routed rebate to allow a single light tape to fit externally, and all the “meat” of the joint strapping is internal. This maintains fairness externally, whereas on the ply boat the internal and external strapping is more evenly divided which requires more external fairing. The composite boat will hold it’s value better than the ply one and offer better investment value and re sale.
This trimaran will outperform our Proteus cat in most conditions, (polars available) since for similar rig size, equipment and righting moment the overall weight is 25% less & wetted area almost 20% less. Admittedly the Proteus cat is more “livable” in a cruising context, with more space and loading capacity.
>The Bruce number of the tri at half load condition, taking main ex roach + 100% foretriangle area is 1.76 and the stability index of 34 against 1.58 and 36 for the cat.
| 9.98 meters
0.45/ 1.656 meters
2800 Kg (with engine, anchor gear, sails etc)
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