fuel efficent offshore boat

[eurotk1]

Due to the fuel prices today I am looking to trade in my high hp deep v for a more economical to run hull like a sharpie , a mullet skiff or a step chine flatbottom.My question is how sea worthy are these hulls?I am interested in building somthing in the 30-34 ft range with a beam of 10 ft or less.Top speed could be about 25 mph but more importantly a cruse of 16 to 20+.Im looking to power with two small 4stroke outboards.Does anyone know of anyone whith plans for somthing like this That i could use off shore?








=

[yokebutt]

How about a catamaran with a more "sailboaty" shape than the planing go-fast type?

Yokebutt.

[tom28571]

Ruel Parker has a boat just like you describe.

Steps, flat bottoms and other such are probably not what you want.

See page two of this forum under "Trawler Concept", post #7 for a design that may fit what you're looking for...

[im412]

for the speed that you want ..i would look at a cat or panga design..
depending if you want mono or multi hull
the best economy is obviously a slower light displacement hull
but every thing is a trade off
jack[a novice]

[eurotk1]

I looked at a large panga but it was powered by twin 200s,Just dident seem economical to operate.

[yokebutt]

Planing is generally an expensive proposition, that's why I was thinking skinny non-planing hulls may have some merit.

Yokebutt.

[eurotk1]

where do I obtain info on ruel parker designs,picts etc.

[Milan]

Here:

http://www.parker-marine.com/

Milan

[yokebutt]

Perhaps, if you're real lucky, you could entice Mr. Speer to offer his opinion on this seemingly contradictory set of criteria.

Yokebutt.

[kmorin]

eurotk1,
If you're @ 30'-34' and moving 16 up to 25 your speed-to-length ratio is 3 at the minimum (gets larger at your top speed) so you're planing with this size hull and your speed requirements. If you plane the hull you're going to need to have enough power to get over the 'hump' and that's not happening with a pair of 50hp Honda OB's on most 30' hulls. Once you're moving a 30'er this fast the entry has to be deep enough to 'live' through the heave and pitch in a swell.

It gets to a design circle here- if the all up mass is very low to make powering economically attractive the pitch will likely become unbearable for offshore cruising. If the all-up cruising displacement is worked around with the bow waterlines in plan then you could find an acceptable compromise between motion and wt to push for the power. Pretty touchy design work- not for the faint of heart or inexperienced as I see it.

I'm not sure your design parameters will be easy to find/refine, if you had a 30'er light enough, with a beam to length ratio slender enough to make your speed goals economically, it seems the hull would have to be so light you'd want to stay inside a bay.

It would be (about) 30' x 5' x 1.5' draught so the 6:1 beam to length ratio would allow you the target speed within the hull length and "light" power. She might be easily trailerable though.

Built in super light WEST, composites or alum it might be done, but it would all work much more easily if you could give up a few knots for this size. I think a boat as light in displacement as implied by 16-20 mph with light power will have such an uncomfortable motion offshore that you'd find it undesireable. On the other hand, the same boat (light, slender, econo power fine entry) might move very nicely at slightly slower speeds even off shore.
Cheers,
kmorin

[eurotk1]

I looked at the parker design and it intregues me.I would like a hull like this as a self bailing center console.you said I would have to give up speed to achieve my goals,what would a realistic cruise be?IF speed increases with waterline how about a 9.5 ft wide 40 ft long sharpie with twin 75s.give it a steep entry with a small angle running surface.Keep all the weight down low and run at moderate speeds offshore.

[kmorin]

eurotk1, I didn't say you had to give up speed to attain you goals- you can travel fast in a very light boat- what I mentioned was the RIDE. Have you ever ridden and old 60's land yacht? like the Caddie sedan or big Old's? Have you ridden them at higher speeds say 80 or 90? If you have compare them to the ride that you'd get from a lightwt auto? Any smaller mass car will behave differently and I was just making the point that displacement AND shape make the "ride".

So if you reduce the wt and keep the size wide and full the bow will rise over a swell and nearly stop the forward motion if the sea state is short sided rough chop as the face of each swell is almost vertical in some cases. If you keep the wt down to make it more econo powered- you're going to have to make accomodations to the shape and expect a 'more active' ride.

Shapies, skiffs, bateau's and were designed to accomodate sail so they're often targeting 4-6 knots except downwind when they surf- 12 would be scooting for these historic shapes- but they'll go faster. I won't try to predict the ride comfort or crew fatique in these shapes at higher speeds- its case by case.

One design idea that will work well is to create a sail boat type hull and flatten the butt lines aft the amidships section where they'd normally begin to rise aft. Harden the chine or even knuckle the chine keep her light and long like Wm Garden's 60' "power canoe" which is a powered dory in Yacht Designs. This boat is an example of the DIRECTION you're headed (not necessarily the prototype) and is worth a look.

D.Gerr in the Nature of Boats discusses the ideas you're exploring better than I ever could, that is also worth a look. Dave covers many of the design cycle items you'd need to consider to evolve a boat which incorporated what you're looking for. He has several suggested designs (examples of his own work as a full time designer and engineer) which you can use to guide you around the conversational 'bush' of related shape, displacement and power.

Cheers,
kmorin

[Corpus Skipper]

One design idea that will work well is to create a sail boat type hull and flatten the butt lines aft

Lobster boat!!???

[Corpus Skipper]

I do have to add, speed is definitely expensive, as well as fuel and drive choice. My 21' walkaround with a single 175 2 stroke got about 1.25 nmpg at 18-20 knots, 3500 rpm. Usually had to run this speed to avoid flying off the wavetops and knocking your fillings out on the landing. (3500 lb. boat) There's that modern lightweight all composite construction working for you So now I have a 26 foot flybridge, twin 270 Crusader V8s, straight inboard 10' beam, 8500# dry, about 10,500 underway (fuel, bait ice, gear, fat boys....). She gets about 1 (that's right, ONE) nmpg at an 18-20 kt cruise, but with a SUBSTANTIALLY nicer ride offshore due to the weight and torque of the inboards (no throttle jockeying) and close to 1.25 nmpg in calm water. Now enter my friend's 26' John Allmand, 10' beam, close to the same weight as my flybridge, straight inboard with a single Cummins 4B, no turbo. It's a slug. 12-14 kt against the seas, won't even think about planing. With the seas it'll get on plane (barely) and do 16-17 kt. On the good side you NEVER pound in that boat, It's a great stable boat trolling or tied up (which is what you spend most of your time doing anyway, right?) and best of all, she gets over 3 nmpg, on cheaper fuel to boot!!! SO, it takes about $140.00 more to take my boat to the same place 5 or 6 kt faster. Get that

One design idea that will work well is to create a sail boat type hull and flatten the butt lines aft

and stick a single diesel in her and you can have your cake and eat it too. Good luck!