20ft Nemesis Cat

I too have drooled over Freeman's they are beautiful boats and according to the net one of the best riding too! The uneven deadrise on the Hammercat is the adoption of the semi-symmetric hull form giving you the best of both worlds. The tunnel is also extremely high out the water at rest.

Mr E, you are right about the negatives of my deep vee carrying all the way to the transom on my design for South African beach lauches giving you a deeper draft. So my draft at rest is just under 400mm (fully loaded), excluding engine draft, which isn't too bad.

More Fat hull sight seeing if you like haha...

 

That has to part of the reason the fat hulls are popular, draw less water. Have a look at the little Kevlacat 5.2m that is highly regarded, terrific re-sale values tells a story, a narrower and taller boat than the Sharkcat 5.6. But no fat hulls.

 

I'd love to have both next to each other and take them out and do some comparisons.

Surely there is also the loss of load carrying ability with the slender hull of the Kevlacat.

 

This is the closest length equivalent to your Kevlacat, the Cobra cat 525.

 

It isn't a problem, I think it they get heavily loaded, the "wet deck" aft starts to come into play. No Kevlacat over there ? They have exported a few, bigger ones probably. The original Kevlacat was a 20 footer, and is still well regarded, I think initially they might have marketed them as a lighter, less fuel hungry cat, but I doubt they could be called a light boat these days.

 

The Cobra Cat is a "fatty" going on those pix ! These boats do concern me a little as regards dynamic stability, but can't be too much of a problem or there would be frequent casualties.

 

What speed can these boats confortably hold plane at ? The Sharkcat 560 it would be close to 20 knots, these fat boat should be less.

 

Skip to the middle of the vid to see them on the water.



18-20kts depending on sea conditions. Not sure what their top speed with 70hp 4's is...

 

Another.

 

I'm not sure what you mean by this, dynamic stability is produced by a combination of the chines and planning surface/area. Surely the fatter demi's will have more planning area and therefor more dynamic stability?

 

Under some wave circumstances a rotational force can arise, 99.9% of the time, OK, it's the 0.1% that gets you. A heeled cat does not get an increasing, nett righting dynamic force on the low side like a heeled vee-hull does, if sent into a rotation.

 

The best prevention is slim hulls and heavy boats.

 

this was an early model 20' shark cat, I would say the hulls would be under 2' wide, and actually I think dead flat at the transom at that stage.

 

I hear you, but the wider sponson will be more resistent to healing, where Sharkcat got it right was to counter the slender hull character they went with a wide boat and a flat tunnel where they regain what's lost. I might be wrong but this is the way I see it. That's why the SA boats can be narrower.

 

It isn't so much heeling as a rotational effect than can occur in unusual wave conditions, confused seas, I'm sure you are familiar with sudden lifting of one side at speed in quartering seas, that is countered by the wave passing under the boat and lifting the other demihull, it is when the rotation continues, like a plane doing a victory roll, but instead of a wave crest there is a trough, they keep rotating. I think you need to mitigate that initial rotation, but I do agree reduced beam will aid that. But I have little doubt the better boat if those surf launches are not required, is the slimmer demihulls boat