Personal Observations on Foils and Skinny Hulls. The research I have done over the past 8 years on Foils and roll motion- testing many powercats in wide ranging conditions, living afloat on cats for a few years has led me to these conclusions: 1. Foils for their extra $25-$70K cost (cost depending on size, country of origin and level of sophistication in trim control) are advantageous for boats wishing to cruise at 28-35+ kts for many hours a year. For ferries its ideal as the payback in fuel saving running 8hrs a day will be soon realised. Pleasure-boats may take a while to get payback VS adding more horsepower but the eco-conscious boater will like it. Depends on the deal you get on the engines on the day. 2. Personally riding on foil boats into 10-12ft head seas at 25kts and feeling very soft landings (a 14m boat) was enough to convince me they certainly improve ride, like adding leaf springs to a vehicle with no suspension. Our 26m Tennant cat would break things in these conditions, even slowing to 6 kts, due to lack of reserve buoyancy in the hulls and knife like fine bows. 3. But by just adding Foils on a slim hull cat will miss a large part of the hull improvement opportunity. Adding fullness above waterline in the bows helps reduce bow tunnel pounding and a foil will soften landings on fast boats, hence our new hull shape was developed after 6 months pounding across the Pacific in skinny hulls bruising the crew black and blue. We and the crew of boat-builders all decided future boats will have less tunnel entrance, 2 months in Tahiti repairing tunnel delamination and core shear gave us time to think this over. (Composite originally engineered by a leading composite design house might I add) 4. Further to the crews bruising was the snappy roll motion of skinny hulls in beam seas. A 16 day voyage from Marquesas to Galapagos with a naval architect, an engineer and 2 boat-builders aboard gave us time to reflect. Skinny hulls are for harbour crossings, not real time, confused ocean seas. Wide hulls we think have slower immersion rates so they don't sink down quickly to the tunnel buoyancy and stop dead, snapping back when the arched tunnel is reached. They immerse slower, finish their roll softer and some weight aloft also helps slow the end of the roll. 5. Performance figures from leading ocean going ferry designers of wide hulls showed their well designed hulls were operating as fuel efficiently as our skinny hulls so naturally we crossed over when we experienced the improved ride. Well designed is the key, some builders have taken old design hulls from old moulds that weren't designed well to begin with and certainly not for the new superstructure balance and make a boat out of it. The hull has to be optimised for the speed, weight and superstructure by a QUALIFIED naval architect who knows how to calculate and computer model it and has done many ferries and pleasure-boats to his credit to compare, not a self taught draughtsman guessing it each time. 6. The people we learnt about wide hulls from and selected for our new hull designs have hundreds of ferries crossing ocean straits in all corners of the globe where stiff penalties for getting it wrong would have sent them out of business. They charge a fair penny but the result is worth it. Kind Regards, John Winter Managing Director Adventure Bay Powercats Cell +64 21 454 107 www.adventurebaypowercats.com

John, Could you define 'skinny' a bit more? What L/B ratio do you feel is optimal, or is there another 'measurement' that you are using? Bob Deering Juneau, Alaska On 11/18/09 12:31 AM, "John Winter" <john@adventurebay.co.nz> wrote: > Personal Observations on Foils and Skinny Hulls. > 3. But by just adding Foils on a slim hull cat will miss a large part > of the hull improvement opportunity. Adding fullness above waterline in the > bows helps reduce bow tunnel pounding and a foil will soften landings on > fast boats, hence our new hull shape was developed after 6 months pounding > across the Pacific in skinny hulls bruising the crew black and blue. We and > the crew of boat-builders all decided future boats will have less tunnel > entrance, 2 months in Tahiti repairing tunnel delamination and core shear > gave us time to think this over. (Composite originally engineered by a > leading composite design house might I add) > > 4. Further to the crews bruising was the snappy roll motion of skinny > hulls in beam seas. A 16 day voyage from Marquesas to Galapagos with a naval > architect, an engineer and 2 boat-builders aboard gave us time to reflect. > Skinny hulls are for harbour crossings, not real time, confused ocean seas. > Wide hulls we think have slower immersion rates so they don't sink down > quickly to the tunnel buoyancy and stop dead, snapping back when the arched > tunnel is reached. They immerse slower, finish their roll softer and some > weight aloft also helps slow the end of the roll.