"Evolve"-type catamarans

[RavellingTangler]

could the experts comment on whether this idea is new (or substantially new, in the details) ?

I'm sure I have seen posts about slim-sponson displacement catamarans before but cannot recall if any of them were displacement-only (not semi- and planing like, say, Glacier Bay which I noticed on one of Roddy's photos had very fine bows....very thin indeed)

http://www.fullbarcomposite.com/

[plankton]

Roger,

there's a whole bunch of similiar designs out there like this now, including the Glacier Bay, which was a full displacement design originally (has it changed then ?).

This particular shape may seem to be a novel idea in British boat-building terms and chronology, but it isn't really. It's a good example of marketing hype at its best. Several other UK companies are there or thereabouts already, especially in the sailing department.

For example, Ecocats > Home


And although not a full displacement cat, this vessel seems to have a lot of promise.

Home

[RavellingTangler]

Thanks, Roddy.
As usual, my ignorance has become apparent (e.g. I thought Glacier Bay were semi-displacement even though I had noticed we'd not got up to the plane ....probably.... on "Gecko" when doing at least 12 or 13 knots).

Can you suggest where I should {start} brows{ing} to get educated ?
For example, are there any publications or websites which cover a lot of new-fangled boat and ship types ?
Where I could tell if the "Evolve" is really just Rod Baker's "Port Isaac 42" slightly changed ?


By the way, heard any more about how the Aspencat (proa) is selling, and doing ?

PS on thsi sideof the Atlantic (and especially in commercial fishing circles) it seems to me that "Cheetah" catamarans have the lead in marketing hype

[Catmando]

Hi everyone

As a newbie to this forum I'd just like to say hi. Further to that I thought I'd stick my ore in on this thread, as I commissioned the design of what is now called the Evolve catamaran (we called it the Evolution when we had it). We recently sold the moulds for this design as they were far to big for us to deal with and were in my opinion not well suited to the workboat market we are engaged in as a company. The design was commissioned as a one off for Southampton Solent University for a student training vessel, and although it worked well, I felt that several improvements needed to be made. This was the last time we dealt with a Naval Architect, and the start of my attempts to get to grips with cat design.
The other interesting fact is that the result of these attempts is the blue and white vessel further up this post! I have dubbed this hull the S.P.E.E.D. Short for Small Power Extended Efficiency Displacement.
As has been correctly noted she is not strictly speaking a full displacement hull as she has lifting strakes, but these are there to help us break 30Kn which is quite hard to do on a vessel this short.
Video of sea trials can be seen on You Tube if you search bwseacat.
Bit cheeky to hijack this thread I know, but there were too many coincidences to let it slide!
One last one. Many years ago I worked just down the road from Rod Baker when he was building his cat plug. The design is not his but comes from Crowther in Australia. Very nice bit of kit. He has paved the way for us to sell boats for sure.
I got into this however from the designs of the late Keith Bennet of the Scilly Isles, who was a close personal friend during the last years of his life. As such, the heritage of our vessels can be traced back over 40 years in the UK.
Interesting stuff!

[MarlinNut]

Originally Posted by Catmando

Bit cheeky to hijack this thread I know, but there were too many coincidences to let it slide!

Not cheeky at all, considering your relationship to the issue in question - especially if you can provide insights!

[Catmando]

Originally Posted by MarlinNut

Not cheeky at all, considering your relationship to the issue in question - especially if you can provide insights!

Thanks

I don't know whether I can help or not with what you want to know, but I will certainly try.
I started out designing cats by looking on forums like this and on the web for different designs and what it was about the successful ones which made them work so well. I guess I maybe know a fair bit now about what makes a decent non planing catamaran.
I beleive 100% in the displacement hull as the best form for the vast majority of applications and would be happy to discuss the whys and the wherefores with those of you that may be interested.

Like I say I know pretty much all there is to know about the 'Evolve' cats. I should do, I built the plug and the mould!
She was based loosely on a series 64 hull design which is a fairly generic round bilge displacement form. She has flattenned aft sections and a knife like bow which means at speed she will cut through the water very well. She did however have a tendency to 'nod' disconcertingly which was due to a lack of buoyancy forward. This can be rectified somewhat by shifting weight aft, but it makes the first third of the hull basically unusable. For a workboat this is not ideal.

I could rabbit on for hours. Like I say, if I can answer any questions about fine entry displacement cats then I will to the best of my ability.

[plankton]

Hello Catmando,

Welcome to the Nut. I'm not sure how many people you will find here who are genuinely interested in power cats, but Roger and I will do our best to keep you busy !

As a cat user, owner and rideruponmany, I concur heartedly with your appraisal of the hull forms and your propensity towards the displacement hull as the best form. I've been aboard many small to medium sized cats in the US, South Africa, New Zealand and Europe, and my summation is very much in agreement with you. Providing you can overcome the lack of buoyancy in a fine entry, the displacement hull gives by far the smoothest ride and best weather keeping for cats. As a vessel gets bigger then gross tonnage comes into play and irons out many of the wrinkles associated with smaller cats and their different hull forms, but for vessels under 30' I would not look anywhere else apart to a displacement hull.

I noticed your BW series a while ago and assumed that they were semi-planing hulls, can you tell me more about them ?

In your travels amongst the Scillies, did you ever meet Barry Philpott ?

[RavellingTangler]

can either of you tell me why the "pointy lower bow" type of wave-piercing cats (like the NZ-made aluminium fast ferries, as used by SeaLink in the UK) have not made it into smaller cats ?
I mean the shape where the bow seen from the side has a sharp point at (or below) water level and another point at the highest level of the bow (so , from the side, it looks like a V has been sut out of a 'normal' bow)

The smallest of those I have seen were probably 12-15m long (as harbour ferries in the USVI) and someone there said they tried making smaller but had a problem with strength, or a tendency to break up in a chop (or short swell) when they got under about 15metres hull length.



Roger

[Catmando]

Hull design becomes very confusing when it comes to semi planing, semi displacement and the worst of all modern terms 'displaning'.
I guess I would describe my hull design more as a 'lift assisted displacement' type.
The idea is that in order to break the 30Kn barrier on a vessel of this size, there is the neccessity to dispense with some of the drag associated with the physical wetted surfsce area of the hull. This drag factor is not particularly important at lower speeds, the biggest factor being the wave making resistance, which is a measure of how easy it is to push the hull through the water.
To reduce wetted area, the vessel needs to lift somewhat, although not to a fully planing attitude, hence the chines or lifting strakes which are visible on my hull. Purists will argue that they themselves create drag, but then most of these people are used to much longer hulls which due to the laws of physics are capable of higher speeds without the need to lift.

I have indeed run into Barry Phillpott and would count him as a friend. His Powercats were very popular and it is a shame that his company folded. The boats are now produced by Darren Newton down at Dazcats in Cornwall.

The answer to why the V like bows are not used is mostly down I would think to production cost on a smaller boat and also the practicality aspect of worrying about a slender hull section sticking out in front. You must remember that the majority of boats these days are kept in Marinas and spaces are quite tight to get into. Also on shorter vessels this bow shape would constitute a fair amount of wasted internal volume forward and so designers in their wisdom would steer clear even though it may produce a more efficient boat. Remember, efficiency comes in many different forms, not just fuel efficiency. There is build efficiency and efficient use of space to consider also.

[RavellingTangler]

Oh yes - it is "obvious", now you tell me.
Thanks

(time to go and look up "Dazcats")