Cat Build (power)

[david1123]

Evening all,

I am planning on building a cat, not my first build by a long shot but cats are new to me so I am going to need some scants to help get an idea and no doubt end up modifying. I have been looking at the Ken Hankinson 24' Wildcat Cuddy. There is some information on the vessel as well as builds people have completed. Some have said the scants are pretty much useless and also voiced concerns with tunnel height (too small) etc. Has any one any further knowledge of this design? My main question is with regard the Stormcat 23'' BoatPlans.com http://www.boatplans.com/cgi-local/shop.pl?cart_id=76d442e6a84699fd0f0e97aabbeaed80&type=item&categ=023&item=1105802689. I would much prefer this design due it having a larger beam (9' 2''), a wheel house and also a more modern design aesthetically. My concern is the fact I cannot find any further information than what is displayed in the above link. No designer name, no images of a completed build e.t.c. Any help would be much appreciated I want to begin ASAP and be finished for next May but don't want to rush into a design. Any other designs to consider would be much appreciated.

Regards,

David.

 

[Mr Efficiency]

Some here:
Plate Alloy Australia - Catamarans http://www.platealloy.com/cats.htm
Kit boats really, but close to your requirements in hull design, probably.
I think a member here, Alik, of Albatross Marine Design, has some stock power cat designs in your size range. You did not mention what material you want to build from.

 

[david1123]

Cheers for the link Im not really interested in buying a kit just looking for plans. She will be a glass sheathed ply affair but I will take mouldings from her so I can build a glass one to.
Thanks.

 

[Mr Efficiency]

The Stormcat design looked likely, on what little was revealed, a front/rear view would have been nice. It is pretty well in line with what is generally available, looking at the profile of it. You would like to see some more detail, though, certainly a transom height of at least 25" would be required. Tunnel height appeared adequate. You are a little restricted by specifying ply, as regards plans, as a lot have shifted to alloy or composite panels.

 

[fallguy]

Make sure and review the Richard Wood's folding Skoota 20 or 24. It is a really nice great, efficient design and it folds, so you get a much wider beam, nearly 13'! You don't get dual engines as it is setup for a single, but the cost savings is there. I am building the Skoota 32DM, which is a much larger demountable version of the Skoota 32. One Skoota 24 at least has been completed with excellent results in speed on sea trials and unbelieveable mileage opportunities as cruise. If you wanted a fixed version or a dual engine boat, the Skoota 28 should get your consideration as well and you ought to speak with Richard Woods to make sure the boat can't be modified to your wishes. All the boats from 30' and under are plywood designs, but might be modifiable to foam. I believe he set the 24' up for a dual camper, but you might be able to make some modifications to make it more of a fishing or open cruiser or work boat. Make sure and talk with Richard. I really like the Skoota 24, but I wanted a boat I felt good about doing the Inside Passage and Bahama cruises. The Skoota 24 I think has a drop down aft section to give it better cabin height at rest while maintaining the bridgedeck clearance underway. Make sure and check it out and ask about changing it if you don't like something.

 

[Mr Efficiency]

Different types of boats, the displacement cat type works up to about 20 knots, beyond that planing forms are better.

 

[fallguy]

Different types of boats, the displacement cat type works up to about 20 knots, beyond that planing forms are better.

To be honest, I didn't realize he wanted a planing hull. If you want more beam, you generally have to give up the planing hull.

Here is a quote from one of Richard's builders. Please note, 8 adults is probably an overload and the boat is probably designed for about 20 knots as Mr. E suggests.

"My SKOOTA 24 was launched last Saturday. It is powered with a Yamaha 50 hp 2 stroke using a 11-3/4" x 10" pitch propeller which gave it 5000 rpm at WOT and a top speed of 28 kilometers per hour. It will probably go faster as the boat was heavily loaded with the sea trial crew of 8 adults"

Here is another catamaran styled plywood boat you can check out. I think all of JMs boats are 'stretchable' to 10%, so you could build it 24'. His deck clearance is 16" above the WL I believe. Wood's cats are generally 20". I know you mentioned deck clearance and beam, which is why I suggested the Wood's displacement design, but Mr. E is right about the slower speed.

Anyhow, here is a planing cat you could stretch to 24' (I think).

Cat 22 (CT22) - Study Plans https://bateau.com/studyplans/CT22_study.php?prod=CT22

 

[david1123]

Cheers for the input guys. I would like a planing hull with twin motors for a relatively offshore boat. Its a 60/70 mile round trip to get out where the sharks live and with the boat I have I'm limited to exceptional weather days and a long slog! So days out fishing in this manner can be counted on one hand for the entire season. I have looked at the plans you have all kindly posted but they do not quite meet my needs.

On a side note I sent the lovely people at boat plans a message enquiring about the ''Stormcat 23' or 23' 7'' to be exact. I asked for the designer and the reply I received was that they didn't know but it is an Australian design and they bought the plans from ''Build-a-Boat''. I have looked for build a boat but no joy. However I have searched for Australian designed cats and if I'm not mistaken the design is very similar to the ''Sharkcat 23' '' designed by Bruce Harris'', Im guessing if so, some our Australian friends may be able to enlighten a bit. From what I have read they are a superb cat.
Shark Cat 23'' 1985 SHARK CAT 7M https://www.tradeboats.com.au/detail/shark-cat-7m-461227 there are various variations on the design but very similar?

The plans are given as alloy or ply, Alloy however is way out of my budget and nor do I want to build a plug and go glass (against my fathers best advice). I just don't see the point. My plan is to build a ply sheathed to keep for myself and take mouldings of her as I go. There are very few cats in the u.k that have a reasonable price tag. Im not going into boatbuilding but I would sell the moulds or knock up some mouldings if there was any interest just to recoup some cost of the build. I know its going to be a long haul project (been there done it a million times) especially taking mouldings as I go. But on my budget I can do it and this will be a keeper boat. Im a bit of a knob when it comes to boats I tend (like my father) to spend months+ building, use for a couple of months get board and want to start on the next. I think I'm just a builder like my dad he is a rubbish sailor (not a novice by a long stretch) but an absolute legend on build and design. However he has never built a cat either power or sail he hates the things so at the moment he is angry with me for wanting to go to the dark side!

Cheers all,

David.

 

[Mr Efficiency]

David, it seems Build-a-Boat still exists. See here:
Powercats http://www.buildaboatplans.com.au/index.php/plans/powercats
I am familiar with the Sharkcat breed, certainly the Stormcat 23 is of similar proportions to the Sharkcat 23, later known as the 700 series (7 metre) This boat originated about 1973 or '74, and for decades evolved gradually, but still retaining much of the original thinking. These old boats have undergone something of a revival in recent years, with the advent of 4-stroke outboards. Previously, a 23 footer powered by twin V6, non-DFI 2-strokes became a liability as fuel prices soared. Now, the fuel bill is somewhat more tolerable. Certainly a highly regarded vessel, as it was the first choice of many marine rescue outfits, water police etc. Also popular with abalone divers. The smaller 560 series Sharkcat was also very highly thought of, in fact one experienced boatie with thousands of hours in power cats of various sizes and makes, described it as the most forgiving of all of them. It is a fully-fledged offshore boat, in just 18 feet. Sounds ridiculous perhaps, but true. The further advantage it had was the ability to run on smaller engines, 2 x 90hp more than enough. It was a much lower profile boat than the 23', and when off the plane could occasionally scoop water on to the foredeck in a joggle, but once on plane, ran like a charm. If you google "old school Sharkcats facebook" you will see there is something of a cult following with these old things. Make sure that any plans you make use of, uses 25" transom height as the minimum, the original 23 Sharkcat used 20" length engines, which was all that was available at the time, and the powerheads were known to "drown" because if it. When the XL shafts came in, the transoms were raised, and the hulls "fattened" slightly. Another issue with power cats of this size generally, is more recently a move to podded engines, that certainly frees up space inside the boat, but the effect on running characteristics is questionable. In fact, some boats do not handle the weight perched further out there, and the remedy of using foils etc fitted to outboards isn't entirely successful. Of course if the pod is virtually an extension of the hull bottom, it is less of a weight problem, though of course the boat is now a different one, with extra length. Transom hung is best if the extra internal space is not really needed.
Although these things are a "killer" hull for offshore work, there were several factors that has limited their appeal. Firstly, twin engines increases fuel use and maintenance costs. Also, the production of a fine mist of spray around the engines from the disturbed water exiting the tunnel, was proven to shorten engine life, with salt spray being drawn through the crankcase in two-strokes, having adverse effects on bearings particularly. This was a live issue, some outboard makers would not warrant their engines on cats. Some people experimented with sealing the outboard cowl, and feeding air through a hose leading into the boat cockpit, away from any spray. I am only guessing, but 4-strokes seem much less affected, with big engine hours being obtained, presumably aided by the crankcase not subject to the salt spray.

 

[david1123]

Cheers for the long informative post, I have read (not sure if correct) about them having pods added due to the modern fours not being able to function in the wells. The design is of the well type with a bathing platform and transom door which I would prefer and wouldn't hesitate in mounting a pair of optimax's in the wells, I haven't a bad thing to say about them. Not sure on size yet. Any recomendations? I have heard everything from min 150's to 200's to 110s to 90s will be fine, Im not a speed demon, enough for the hull to perform as designed plus a little extra for when needed will suit me fine. I will enquire as to the transom height, it's not to much of an issue I can make alterations.

Thanks,

David.

 

[david1123]

Just thinking out load seeming this will be my first Cat, Would a standard outboard set up be ok or would I need the props turning in opposing directions. If so what would be preferential, props turning inward or outward. Im just thinking about torque steer and prop walk at low speed/reverse e.t.c.

 

[Mr Efficiency]

Without knowing the dimensions of the Stormcat 23, in particular the width across the chines of the two hulls, it is hard to say what power would work best. Fatter hulls with a narrow tunnel requires less HP, If the hulls are around 24-25 inches wide, and the boat is going to be around 2 tons upwards, you will be better with engines around 2x15o HP (XL) or a little more. That should give a cruise speed in the high 20's, knots. You don't need the high-thrust variants that are available in some motors, they will cost a little extra fuel, by losing some speed. You do not really need counter-rotation, boat lean due to prop torque is not a problem, and steering feedback can usually be eliminated by trimmimg the engines. However, you would be better to use hydraulic steering, that way you get the full trim range of your engines without having to fight the wheel. Also, check the transom rake is at least 16 degrees, to get sufficient trim-in, which is desirable to have at your disposal at times. Optimax is a great engine, but on cats, I don't know, as I mentioned it still draws intake air into the crankcase. I think I would go to four-stroke, probably Mercury 150 as the weight seems to be less, and the maintenance cost is less. But I would like to know the width of those demi-hulls, if they are quite slim, the extra weight aft could be a problem. I include a rough sketch of the general shape and dimensions of the Sharkcat 560, which might be of some use as to a benchmark of what works well.

 

[david1123]

Message sent I'm not in to much of a rush to begin, I sent a message requesting the dimensions so we shall see if the company oblige. I was thinking around 150's as a mx to be fair, I have noticed in the specs the boat weight is 3.8 tonnes! That surly can't be correct. I know the sharks go around 2.1 tonnes in glass and un-fueled so Im not entirely sure what the weight of a glass-ply will come in at. As mentioned, and thank you, I will keep an eye on the misting problem. I would prefer to keep the OB's transom mounted so if space is an issue with four strokes I will do as suggested with twos's and run some intakes into a mist free area. Definitely going to be using hydraulic steering the morse stuff is just to restricted in such an application. On the counter rotating OB's thats good to hear and I had envisioned it being a trim able fix. Im currently pricing up (roughly !) its within my means to complete but somethings may have to wait for example touch screen electronics, electric windlass, eberspacher. Luckily with dad being a boat builder (retired) I have tonnes of stuff which does add up cleats, bollards, farileads, navigation/interior/exterior lighting, wiring, switchboards e.t.c its all great but the best is his stock of hard wood he has a tonne of Honduras Mahogany and also Teak which I will be framing with.

 

[Mr Efficiency]

I saw that weight of 3.8 tons and if they are talking unladen, seems way high. 23' Sharkcat would go about 3.5 tons on trailer, motors, fuelled up. Ply and wood should be lighter than glass by a good margin. 2x150 will push a bigger cat than this. But going smaller depends on the boat weight, and crucially the width of the two demi-hulls, fuller hulls=less power needed. Not a fan of fat hulls though. Anyways, they might have a drawing of it with the front/rear view. As for the sealed cowls/air hose idea, I have seen it done with several boats, never tried it myself, one has doubts about the safety angle with fuel vapours inside a closed space, should be OK, but I am not 100% on it.
You might like to contact these people.......
Bowdidge Marine Designs / Our Boat Plan catalog http://www.bowdidgemarinedesigns.com/BOAT_PLANS.html
On the website they say plans for power catamarans in wood/ply are "coming soon".

 

[IronPrice]

You might like to contact these people.......
Bowdidge Marine Designs / Our Boat Plan catalog http://www.bowdidgemarinedesigns.com/BOAT_PLANS.html
On the website they say plans for power catamarans in wood/ply are "coming soon".

Those plans have been coming soon for quite some time. Mark's boat designs have great reputation among people that build them and he is a very busy man.