12 m sportfish hull design

[vander]

Hello,

We sold our old sporfisher boat (attached file) and we want to take some suggestions from you .

The old soprtfisherman had Lh: 10,50 m and Beam: 3,75 m.

I attach the drawing of the old boat.

As shown, this hull was a semidisplacement, with progressive vee aft to flat bottom at the transom.

This boat has a full displacement of 9 Tn. ,21 kn max speed and 2x250 HP engines.

At this moment, in our shipyard we want to make a new ONE-OFF GRP/PVC boat for fishing in our area; North of Spain, Atlantic coast.

We use to fish 30 miles from coast and the worst weather for fishing will be up to force 5 and 2 m height of wave.

We are looking for a Lh: 12 m and Beam: 4 m boat, similar to Rivieras, Bertram, Luhrs or Vikings but we have doubts about hull shape.

We are thinking to make a hull, with a little progression, from deep at the bow and littles less angle astern, looking for good behavior riding the waves and more space on engineroom.

I am thinking that vee hulls have more movement when the boat is stopped on the sea, and we are looking an equilibrium between riding and standing on the sea.

For this boat we are thinking to put 2x450 MAN engines and reach cruising speed between 20/25 knots with 12 Tn of displacement.

I don't have much experience about deep Vee boats, because we use to design displacement or vee/flat boats for professional fishing, and not more than 20 knots of speed.

I would like to hear some suggestions from you.

Best regards

Vander

[marshmat]

Are you still thinking semidisplacement then?

Deep- and Modified-V hullforms are best run on full plane; both will be horrendously inefficient at semidisplacement speeds. If you go planing hull in a boat this size, you'll have a pretty big chunk of the speedometer that's unusable; you can't cruise a planing hull at speeds between displacement and full plane.

It sounds like you're talking about an evolution of your old boat design. I'd like to hear what the rest of the forum crew have to say....

[yipster]

yeah.... at least you still have the plans, nice boat

[tom28571]

There are over 40 yards on the coast of NC building offshore boats like that for fishing the Gulf Stream. Almost all are semi custom jobs built of molded ply/epoxy composite. I have a designer friend who has done plans for 20', 40', 50' and 60' models. All are fine entry V hulls with a lot of flare forward and shallow deadrise aft for planing. Most have a bit of aft rocker to hold the bow up when running downwind in waves. This type has been evolved over many years.

[vander]

The idea is to make an evolution from the old boat, desingning little more vee aft and having less trim in the base line, to avoid the bow going up at speed.
Also I have some dobts about stringers. Perhaps is better to make the stringers more paralel to the WL and avoid the wave produced at medium speeds at stringer/WL intersection. With this, also we have a good flotation beam throught all the model, to avoid too much inclinations whe the boat is standing on water. Something like attached drawing.

Regards,

Vander

[tom28571]

Vandy,

For inshore boats, I agree with your thoughts. The evolution of the offshore boats I mentioned takes a different course though. They often must run downwind in waves to get back to shore or outrun weather. The bow down attitude that I might like for calmer water can be dangerous in big waves. I was at first critical of the small aft rocker for efficiency reasons but have come to appreciate the need for it from a safety issue.

[vander]

Hello,

I attach some preliminary from maxsurf.

Best regards

Vander

[RANCHI OTTO]

The top speed seams to be low...
with displ = 9000 kg and 2 x 250 hp the estimated speed would be 26/27 knots abt.
Perhaps propellers non opt.?
Not clean hull?

RANCHI Otto

[vander]

Would be propellers and weight.
Looking at waterline, at this moment, the boat would be at 11 Tn. of displacement.