Efficient cats

Questions and Answers about the Woods Designs, multihulls and others.
Saqa
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Re: Efficient cats

Post by Saqa » Tue Dec 30, 2014 11:55 am

Thanks Richard, thanks for the added info on fuel economy too

Regarding the Skoota 20, can it be fitted with twin 4 stroke outboards? How big?

What kind of cruise and top speed be likely?

With that motor config, will it be ok for 2 fishing + skipper?



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Re: Efficient cats

Post by jacquesmm » Tue Dec 30, 2014 1:09 pm

I'm glad that Richard jumped in because I was going to discuss a boat that I would probably not design anyway. :)
I have too many other projects but get easily enthusiastic about good looking boats like that Sliver.
I like the discussion and want to remind you of the difference between displacement and planing hulls. While a displacement cat with fine hulls will go much faster than a displacement monohull (thanks to it's fine hulls), it is not going to get the same top speed than a planing one. It is still a displacement hull.
The efficient cat as in the title of this thread is a displacement cat going at a reasonable speed for it's hull shape and (without doing the math) is probably 10 to 15 knots for a 28 footer. The best mpg is at less than 10 kn. Top speed can be around 20 kn but at WOT. The faster you go, the more fuel it will cost and I am glad to see that you reduced your speed goal to 15 kn.
You'll need less HP.
Just to illustrate that, I was part owner of a cattlemaran (a 55' day charter cat), a modified Wharram. I remember the boat easily doing 7 knots with a single 10 HP. Later, we installed a 50 HP but the boat never went faster than 12 knots and that was at WOT. Most of the time we were motoring at around 7 kn. whatever the engine.

I think that for your program, the best boat type would be the Skoota 28 without the cabin. It should not be difficult to build her without the cabin.
I plan to post study plans for the Skoota 28 next week.
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Re: Efficient cats

Post by SalmonMan » Tue Dec 30, 2014 4:44 pm

jacquesmm wrote:I like that Sliver 29 and would design something in that style.
I'll read more about it.
I've been looking for a designer to come out with plans for a offshore displacement cat like the Sliver 29 for some time. For me it is the future for offshore fishing. The twin 250 HP outboard deep vee hull boats are too expensive of an investment and
too costly to fuel.

I bet if you would design a version of the Sliver 29 it would be a good seller. The cost of a Sliver 29 from Supercat in South Africa is close to $200k and their Supercat 38 Sport Custom is close to $300k. These plans would sell so please design it!

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Re: Efficient cats

Post by britt » Tue Dec 30, 2014 5:13 pm

Jacques,
That supercat is one SEXY BEAST!!! You or Mr. Woods need to design something like that! :D

Britt

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Re: Efficient cats

Post by jacquesmm » Tue Dec 30, 2014 5:29 pm

I am certain that Richard Woods 28' Skoota can deliver the same performance or close but I suppose it is the aesthetics that get everybody excited . . .
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Re: Efficient cats

Post by Saqa » Fri Jan 02, 2015 10:04 am

I agree with Solman, Cats like the Silver 29 are the future for offshore fishing. Especially for charter operators, it can make for a cheaper charter for the customer meaning more customers with return business and for the operator cheaper initial costs due to smaller outboards and cheaper running so more dollars in the pocket. A win win for operator and customer

The Skoota 28 seems to be a decent craft and could well be a contender but more work is needed in my opinion. A highly motivated builder like myself could possibly convert the layout to suit serious fishing but a lot of builders would prefer building it all from plan

As a starter the hulls and motor combo have the potential. Taking away the living arrangements and transferring some of that weight to even stronger hulls overbuilt for daily commercial use. A simple central driving position with under canopy seating for customers, all around decks with rails for fishing from is needed. I could only find one video of the Skoota 28 that shows it underway from another vessel. It goes very well but to my eyes there is a difference in the body language between that and the Silver 29. The Silver seems to aggressively eat up the waves, rocking less then the Skoota in the vid. Will be good to see more vids of the Skoota taken from a boat that can stay ahead and to the side and with bigger motors on the Skoota then 20s showing the hulls at full potential

I really think there is a place in the market for a build from plans for a serious offshore fishing boat that is fast and efficient. Mr Woods has hulls that are contenders and Jacques boats are well setup for a fishing layout. I would love to see a collaboration from the two in bringing us the ultimate fishing boat. Especially if the guys design around synthetics like honeycomb. Its already a complex build project, it has space in it for added performance features. The Skootas have full waterline lengths and Richard is no stranger to dagger boards and rudders and such. I salivate at the thot of simple L foils under the Skoota hulls working in tendem with especially designed wings on the outboard cav plates lifting the hulls a touch reducing wet area but keeping the full waterline length! With just a little foil assist should outrun and out handle the SIlver!!!

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Re: Efficient cats

Post by Woods Designs » Fri Jan 02, 2015 6:20 pm

As you might have guessed, Jacques and I have been discussing your ideas over Christmas. It is a timely discussion as I have had others, besides yourself, interested in a outboard powered offshore fishing boat. As I said before I know nothing about fishing, while any design changes must match what you can do with a sheet ply boat.

Also remember that a boat is not just for fishing (or living on board or sailing) it must be a practical all rounder, most of the time a boat is not actually going at full speed, whether it be a cruiser a fishing boat or a day racer. A successful boat is one where everyone can relax all the time, whatever maneuvers are being performed. That means no shouting, no stress and people are happy to go out with you again.

For example, and using the Sliver sketch to illustrate: The boat is a moulded grp boat, so has lots of double curves for stiffness. Looks good and "sexy" but is much harder to make in wood. That's why my Skoota has a flat upper topside (in purple on my boat). Years ago I draw a grp powerboat with similar curved sides, but it only really works as a production moulded boat.

But also relevant is that my flat panel design is not so curved that it is impossible to board. My acid test for any boat is "could my mother get on board" - too many boats have too much tumblehome, or high freeboard or no transom steps, you get the idea. Another acid test is "what if it rains"? Must be something about being English I guess!

So I think my mother (not to mention Jetti, my wife) will struggle getting on board Sliver from a dock - from a dinghy it would be easy. Not only that but Jetti no longer "does jumps" which would mean I'd have to be very good at manouvering the boat when coming back to the dock. It is not really possible to jump ashore. I always like wide foredecks for that reason and usually put the pulpit 18-24in aft of the stem so people have somewhere safe to stand outside the lifelines when coming into a dock. And of course it's why I won't draw reverse bows.

So: Do the Sliver fishermen fish from the windward side, the aft rail or with lines out port and starboard? Where do they sit/stand when motoring out to the fishing grounds? Do seats get in the way when landing fish? The cambered sides won't help - surely you want the cockpit edge to be as close to the gunwale as possible? When landing a big fish do you "back down" to it? and if so does the transoms/engines go underwater as you do? Surely higher freeboard aft (as on Skoota) is a good idea?

I could go on, but as you can see I know little about fishing. However I do know about efficient hulls that run fast with small engines and with good mpg. So our Skoota 28 will 5 adults on board does 15 knots with twin 20hp outboards, despite having a "live aboard" interior. And, as I said earlier, we have found that our Skoota has the same 5-7 mpg (depending on sea state) whether we run at 10 knots or 15

Although I don't know about fishing Jacques does, and so between us, my hulls and his deck layout, I think we could produce the ideal boat for many people. All we have to do is find the time to draw it (although, as always, a couple of orders would offer us encouragement!)

I hope that helps the debate

Richard Woods of Woods Designs

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Re: Efficient cats

Post by jacquesmm » Fri Jan 02, 2015 7:44 pm

And that is why I asked what were the characteristics of the Sliver that made it so appealing.
Form should follow function and Richard explained well the reasons for a certain shape, for some features. Something may look very pretty but not be all that practical and that matters very much for a professional fishing boat.

The material also defines the form. We, and our amateur builders, are working with plywood or foam sandwich. We don't produce boats in a mold.
FRP shapes produced in a mold need all those curves for stiffness.
Shapes for developed plywood or foam sandwich will be different.
No problem with designing a boat for that program but she will probably not look like the Sliver.
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Saqa
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Re: Efficient cats

Post by Saqa » Sat Jan 03, 2015 5:33 am

It really is good to see the cogs turning! :)

I should mention that I have been looking for a boat I can build for over a year now and due a lack of available designs that fit my needs I have taken to studying and trying to build something on my own but since I am not educated in naval architecture I cannot safely design scantlings or reinforcement parts on this scale for a 30' boat. I do have some lines I drew that can help picture the looks I find appealing. Due to many years in the fishing industry and as leading the committees on multiple fishing clubs in Aus as well as being a sponsor on fishing forums in Aus and US I can draw on experience in layouts required for how fishing is evolving. I can also draw upon ideas from operators and fishos in real time

I like the layout approach Jacques took with his pontoon cats by offering a usability that can be highly customized by various users. The point is though the lack of a build from plans for a serious hardcore fishing efficient cat, I am sure the cabin can be extended and more cover provided depending on usage

Richard, your skoota 28 hulls in ply construction doesn't give much away to the Silver hulls in aesthetics in my opinion. To my eyes its the aesthetics of the superstructure that makes the difference. So lets look at functionality and optimise form from that

Lets number the issues so they can be addressed in a controlled manner. I might have to type a lot to make cover all the aspects :)

1 - Hulls; Your hulls are perfectly fine performing and look good and some slight changes to sheer, that can be easily implemented with flat sheet building material, can look deadly too!! Predatory racey looks can inspire confidence in offshore ability

When I was trying to draw lines I drew this shape which I found very visually appealing. I don't have the knowledge to comment on the seakeeping ability but the hull measurements and lines are in range of similar things out there. The simple cad proggie shows a 6" draft for 1000lb displacement for just one hull which should mean 2000lb ability at the same draft for both hulls

Imagelines2 by jonny.toobad, on Flickr

Imagelines by jonny.toobad, on Flickr

2 - Build material; Be really good to either build with ply or pp honeycomb especially for my application where I don't want natural materials. I have been researching this and seems pp honeycomb can be stitched over frames just like ply

3 - Power; Richard has power sorted. The skoota 28 appears to deliver efficient performance and the motor range of twin 20s to 60s is in the sweet spot. I don't think we need to worry about this aspect too much

4 - Accessibility; May be I am being too simplistic but I would have thot a ramp that can be extended out either the back between the outboards or the side through a gate in the rails like Sydney ferries would do the trick. A horizontal ramp that has folding step ladder at the end which can be deployed to suit variable dock heights

5 - Fishing layout; I will expand on this by breaking down forms of offshore fishing as they have evolved on the international scale, after presenting ideal layouts

The new concept from Sunreef shows a layout that I feel is a good starting point for an ideal layout

Image281,_h04 by jonny.toobad, on Flickr

Flat deck with central driving position for skipper. Seating for 4 fisherman and a highly mobile deckhand making for 6 onboard max. A simple cabin structure with overhanging roof to the back would serve fine on a fishing charter

Crotch height rails all around the deck area with toe rails. Gunnels to that height are nice like on the Sunreef40 but rails do the job just fine

That Sunreef also has implemented boarding very well. That platform will aid landing large fish very well for either keeping or release

Side decks should be good sized to allow walking around the boat while fighting a good fish, enough so the deckie can be off the shoulder of the angler ready to assist or call directions to the helm

The Supercat 38 pics below show good layout for seating and all around walking/fishing access. My only problems are the tall metal poles fitted to the gunnels. But that is not a design issue, more like poor fitting out
ImageTHE GAME CHANGER (105) by jonny.toobad, on Flickr
ImageDrop_UR_Rods_(08) by jonny.toobad, on Flickr

Insulated fish storage bins in each hul catering to a paying charter for 4 customers so about 400L each

5A - Game fishing; This is the traditional trolling with large overhead reels on short rods around 5'. A cat has an advantage here over a mono with the spread of lures. Fights are mostly from a standing position. Backing to a fish is becoming less and less common with new age tackle and smart skippers. A cat doesn't have a full beam immersed transom like a betram and with a higher open deck layout is a lot dryer then a monohull when backing onto a fish is required. Further to that take a good look at the Silver under the waterline at the transom. I don't know exactly why they employ that inverted gradient there but if that boat opens throttles on reverse gear, surely that shape would create some lift possibly keeping outboard cowls above water
ImageR17 by jonny.toobad, on Flickr

5B - Jigging; Short rods around 6' and small but powerful reels running 50 to 100lb spectra. Heavy knive like lures are free dropped to the bottom fishing structures like wrecks, rigs and reefs. And wound up with a butterfly type jigging motion. For targeting everything from ground fish, pelagics like amberjacks and even a good way for large tuna like yellowfin and bluefin. Both sides of the boat can be fished from

5C - Popping; Throwing heavy plugs to 200g or more using 8' rods with spectra lines around 100lb size. These plugs are worked back to the boat with violent sweeps of the rod. On open bluewater chasing tuna, the boat is pulled up to the side of a surface feeding tuna school. The angler walks to the opposing side. Drops the lure to near the water surface and casts out over the deck to the school. After casting walks to the fish side and works the lure back. With tropical reef popping its the same kind of deal but stopping outside a fringing reef with white water breaking over the top and casting towards it so again from one side. Wind direction is not usually a bother with the heavy lures used and having to stay on the outside wind is best kept pushing the boat away and slow motoring and idle used to keep in range

5D - General heavy tackle bait fishing and bottom fishing; All sorts of medium to heavy gear used for the styles A-C and either dropping cut or whole baits to the bottom or down current or trolling under power. This type of fishing is not usually an objective of paying customers looking for hardcore action but regularly used by private owners relaxing on the water or looking for a feed

A-D can all see an angler connected to a large fish with heavy lines and having an arm wrestle walking all around the boat

Its a lot to read but optimising 1 -5 could mean a breakthrough boat design when it comes to offshore fish-ability with efficiency. Thanks for your time guys

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Re: Efficient cats

Post by Woods Designs » Sat Jan 03, 2015 10:37 am

Thank you for all that stuff I didn't know about fishing. How do you cast with a full bimini fitted? Do women ever go fishing, or is it just men? How about separate "facilities"? The sketch you show seems to show a lounger for two bikini-ed girls, not four hairy fishermen

Obviously short boats with full standing headroom never look as good as long open deck boats. And it is worse on a catamaran as you have a floor well above the WL, not below it. So you are right, a lot could be done to improve the looks of a Skoota if it had an open deck and no accommodation. My wife and I will be living full time on our own Skoota when we get back to Port Townsend, Wa in March. My wife really likes the Skoota and living on it, which obviously was a very important factor when I designed it. No point in drawing a "sexy" cruising boat if I have to live on it alone!

2000lbs displacement is clearly not enough for a 28ft powerboat that takes 6 people, the crew will weigh 1200lbs, the engines at least 500. BTW what range under power would you be looking at? How far do you motor at full speed to get to fishing grounds?

I see the other powercats have opening doors in the topsides for access. Obviously the foils would prevent beaching or shallow water fishing and presumably act as "magnets" for fishing lines

I do have extended Skoota 30 hulls also available which might well suit you better

Thank you for taking the time to help our discussions, I hope others will join in. I'm sure Jacques also finds it very useful, so we'll keep you posted as we progress.

Richard Woods

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