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Author Topic: express craft 58" thundercat catamaran  (Read 5420 times)

BOATSANDBIKES

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express craft 58" thundercat catamaran
« on: September 08, 2015, 08:43:28 PM »

Hi just got new toy bargain flea bay 50 not in bad condition under side perfect bit of a tidy up then custom paint job something a bit different.single 26cc going in for now twin rudder surface mount propeller doing build blog on it  :-)) :}
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #1 on: September 08, 2015, 08:46:37 PM »

Here's some pics  :}
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #2 on: September 19, 2015, 07:51:26 PM »

Flatted back nightmare very 90s metal flake took a while,had to tidy body work up and cut out windows had some spare motorcycle visors perfect contour for window,also check some data on line it says engine should be fitted 13 and a half inchs from transom to centre of spark plug for single 26cc with off set rudder to help with left hand turns.Does that sound right or is engine a bit far to the rear?
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derekwarner

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Re: express craft 58" thundercat catamaran
« Reply #3 on: September 19, 2015, 11:04:40 PM »

B&B.....that 13 1/2" dimension is interesting a it implies the positioning of a critical weight mass  ;)...however a google search on "single 26cc" provides many options of physical shapes, sizes and assumed variations in mass  %) .... Derek

https://www.google.com.au/search?q=single+26cc&rls=com.microsoft:en-AU:IE-ContextMenu&rlz=1I7NOOH_enAU530&tbm=isch&tbo=u&source=univ&sa=X&ved=0CCMQsARqFQoTCIaGmNaKhMgCFQaMlAodQNwOVA
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Derek Warner

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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #4 on: September 20, 2015, 06:54:17 AM »

Your cog needs to be around 30-32% from the back of the boat on a cat,do not use that measurement as the position to put the spark plug that's a mistake many make.What you need to do is install the hardware first then sit everything in the boat including fitting hatch then balance the boat,once you find the right cog mark and install the motor and everything else where it needs to go.That 13 1/2 measurement is way off,the pipe would be then hanging out the back a lot. COG on a 58" boat at 30% is 17.4".
If it were me i wouldnt use a twin rudder as the extra rudder is only creating drag,id use an offset rudder for better performance ,but if you do use twin rudders be sure they have the ability to kick back in case you hit something in the water like most single offset rudders do or you can rip the transom out of your boat. Also use a skegged strut like this one on one of my 50" Thunderbolts,it really helps a cat in the turns.You will find that on a cat turns will still be good both ways even with an offset rudder,especially using the skegged strut.
The Thunderbolt i build is the same as the Expresscraft hull,Tom allowed me to add this to my lineup and almost everyone prefers to use the skegged strut over non skegged,heres one of Toms that was built using an inline setup,might give you some ideas for the future lol.
Oh nice find by the way ive been looking for one of those for a while lol.A friend in Canada has built a few of those some of them twins side by side staggered setup,same cat under another name,he seems to like them and actually he has used twin rudders before so if its what you prefer looks wise go for it.If i can find them ill post a link to some videos of his builds i think you will like them.
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #5 on: September 20, 2015, 07:04:31 AM »

Heres the videos check em all out youll find something of interest im sure.
Mart
https://www.youtube.com/watch?v=yH1dh0G5Kkc
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Jerry Hill

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Re: express craft 58" thundercat catamaran
« Reply #6 on: September 20, 2015, 09:06:06 AM »

Looking good so far mate.

I won't comment on the engine position because I'm not familiar with the hull, Mart is right as default so it's a good place to start, but if there's any tapering in plan profile on the lift area of the hull, change in the deadrise angle, or through the configuration of any lift strakes it could be different. A pic of the hull bottom may help.

Twin rudders look trick which is a good enough reason to have them, but efficient it isn't. You certainly don't need them, most boats are fine with a single offset one, but there are a few which won't turn Right well, usually monos suffer most. It's all about hull design and what you end up with on the propwalk front.   Having said that two rudders won't necessarily  fix it. If you do go for twins in an ideal world they need to be offset so that they match to turning radius. This just means that the rudder on the inside of the turn needs to have moved a bit further than the outer one, they can resist each other otherwise causing extra drag in turns and losing effficiency.  If you are using wedge rudders this is more important.

Just in case, It's wise to put flotation on the hatch (as well as the boat).

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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #7 on: September 20, 2015, 10:08:48 AM »

As I new to building boats thank you so much for advice,will now go single off set rudder and also use the advice on engine and hardware position going surface mounted on propeller as will be faster and might get nice rooster tail.I'm useing crrc pro GW26I engine got I nice exhaust called stage 6 big beast when I finished mirror polish bits will put picture on plus of paint job.Thanks again for advice  :-))
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #8 on: September 20, 2015, 10:12:49 AM »

From what people have said about the Thundercat it tends to run quite wet for a cat and needs a lot of power to get any real speed from it probably why Randy seems to like the twin setups,even then they run wet.
Another consideration is ,is it the Expresscraft version of the hull or the Forabuck (Vern Kilmer) one which is the one Randy used which do tend to be heavy in comparison not always a bad thing though :}   if you have the power to make her move  :embarrassed: .
The one positive thing about this cat is its very stable even in quite rough water.
Pretty sure Mark Wild has one or did,he might comment and give you his opinion on the hull.The design has been around for years so it might not be the fastest cat out there but should be a very stable platform to work with.
Mart
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #9 on: September 20, 2015, 10:29:14 AM »

Thanks bud got her up and running with one for now the end of next year twin engine refit.video link was brilliant they turn well like you say,thanks again mart when your new to this its a bit of a mine field to workout just glad of some advice  :} :-))
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #10 on: September 20, 2015, 02:06:25 PM »

No worries mate glad to help,also if your on FB i have a group page on there for my hulls.Always people willing to offer some advice on there as well. Plus you can see my boats too lol  ok2 .
Mart
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #11 on: September 20, 2015, 04:34:16 PM »

Right pictures of underside as you can see nice and tidy now wasn't but stopper and rub down sorted chips out.masking tape on transom is that the best place for surface mounted propeller shaft to exit hull or will it want to be higher up the hull?feeling so much better getting advice want to get it done now inbetween other builds 3 weeks hope fully be done but don't hold me to it  {:-{
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Jerry Hill

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Re: express craft 58" thundercat catamaran
« Reply #12 on: September 20, 2015, 08:18:47 PM »

You know a bit about paint don't you I can tell  ok2 .


The strut bracket height is about adjustment. There's two schools of though about the starting height for the strut itself, some say prop centerline in line with the hull bottom, some say bottom of strut in line. The latter seems more common though, it's what I do, from there the bracket height should, in my view, give one quarter of it's scope of adjustment down, and three quarters up. The reason being I find most go up rather than down during tuning, and if you go too far down it's heading into semi surface drive. Your strut should have a slot in it for this adjustment, offer it up and see what prevails.


By the way I note your hull has lift pads, I'm feeling the CoB might need to be further aft than some.
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #13 on: September 20, 2015, 09:03:34 PM »

Thanks jerry for reply so might need engine mounting at 34% or 36% of length of cat.I feel so thick don't know what lifting pad is?.I think I will get a good adjustable strut and 6.35mm propeller shaft then check with you guy with it mock up on boat.Jerry how did you guess I know a bit about painting,up till 3and a half years ago I use to build and paint custom motor bikes.Then I had 1 big stroke and 3 smaller ones which made a mess of right hand side of me.Not being a drama queen but I hit a big low took 2 years of feeling sorry for myself to kick myself in my pants.Wife got me a project boat and I slowly got interested in them now love them.Painting is what I'm good at very good,40 boats now waiting for build ups as painted or repaired and painted.I so glad there is guys around like on mayhem forum to help me learn about build side as I've not got a clue.There one way of repaying members back if any one needs a boat painting or advice let me know also if any one here needs paint best man at my wedding owns paint factory I get it for next to nothing,don't want to make anything from it just helping people back.Sorry for tales of mike but some times things make a differents now feel fire in my belly to learn thanks for help and advice doesn't cost any thing but makes a differents  :-)) 
 
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Jerry Hill

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Re: express craft 58" thundercat catamaran
« Reply #14 on: September 20, 2015, 10:01:38 PM »

We were talking in PM's about blending clear mate, but apart from that I've a history in bike painting myself and the signs are there in your work. People who paint bikes work to greater detail than car sprayers, and I reckon you're using 4:1 2K primer there, pro stuff.


Lift pads are simply flat areas, often raised, on which the hull sits when at full chat, they are a more direct way of achieving lift. But, the prop also creates lift and I can imagine that the rear of that boat will come up readily, hence shifting the weight back. A boat's balance point is just a matter of center of mass, this used to be called center of gravity but with wider eyes it's now better to discuss mass in the absence of gravity, apparently  %) . That's all very well, but a boat's attitude in the water is also dictated by the hydrodynamic effects of water bearing on the shape of the hull. A static floating hull exhibits what's called a Meta-center, which is basically the center of the various mass and flotation forces acting on it. It's often in a different place, especially on planing hulls, and it moves according to the lift being experienced at a given speed. If it ends up in the wrong place the boat will either porpoise like mad if there's not enough speed to get through that, or run wet and heavy in the water.


For your boat though, and indeed with most, it's better to err towards rear weight than forward, as that is easier to adjust in the lightest manner. I.e. if ballast is needed then a little weight way up in the bow adds less to the boat overall than a lot of weight that would be needed aft, simply because there's more room (lever moment) up front to move the weight further for effect.


So, I guess Mart's 30% (from the stern of the boat) is where I'd be looking, given what I know of yours, as starting point.
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #15 on: September 20, 2015, 10:13:17 PM »

Heres a cpl pics to give you an idea on how and where your shaft needs to exit the hull,basically once motor is installed and you get a nice angle so you can have a nice smooth bend in your flex tube this runs under the tunnel and enters the back of your strut.
When strut is installed the prop needs to close to level with the bottom of the ride pads on the sponsons (ride surfaces of the boat) you can adjust up or down to alter how the hull runs.Usually 1/2" up from there seems to work well but each hull is different.
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #16 on: September 20, 2015, 10:20:59 PM »

By the way the bottom of your cat has similar pads to the Thunderbolt ,ill email Randy and ask him where he likes his cog ,hes built dozens of them so should know what works.
Mart
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #17 on: September 21, 2015, 09:16:37 AM »

Thanks I understand now,the hull bottom is like your it already has wooden runners mount for engine and radio box I think engine needs to go in about the same place as yours bud,your right 2k high build primer don't use anything else bud 2k cellouse sinks as only calm and resin,its not asbad to use as people think no need for air feed mask 3m do vapour mask which keeps gases out 70 hours spray time per mask that's a long time for guys at home.3m at spray shop retail for 30 I get them for 10 that's cost price.Also 2pack onces set will not lift if petrol spills on it cellouse will.I forgot about blender sort it out this week I've written it down as memory is rubbish part of stroke thank you bud your a gentleman set facebook up today that's written down too  :-))
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #18 on: September 23, 2015, 09:18:02 PM »

Here's engine I'm going to be useing,and pictures of wooden engine mount tunnel.exhaust had label on it stage 6 its 14inchs from end of pipe to end of pipe but don't like downward face exhaust pipe so slash cutting it so length will be 12and a half inchs its 7and a half inchs round came of 2 stroke boat engine, can you get s shaped exhaust link pipe?
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #19 on: September 23, 2015, 09:21:51 PM »

Picture of exhaust
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Jerry Hill

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Re: express craft 58" thundercat catamaran
« Reply #20 on: September 24, 2015, 12:25:06 AM »

The curved pipe on the silencer is probably the inlet mate. Depending on the internals of the silencer that may be important. If it's a simple can then it doesn't matter.

Yes you can get S shaped manifolds, specifically to bring an exhaust back on centre. This is a basic sports engine and so long as it's not restricted the exhaust system can be pretty much any configuration you want without impairing performance. I've seen many systems cobbled together through welding various bends to make the header of something that isn't on the shelf, and they work fine. Only a high performance engine needs detailed and accurate tuned pipes to get the best out of them, although any two stroke engine benefiting from a tuned pipe is true it's not a requirement for an engine like yours. I've got a few such engines for boats and a few more in chainsaws and strimmers, they all work fine with all manner of exhausts.

Recommendation: Run Extralube ZX1 in your engine, it'll love it. But don't use it till it's run in.
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #21 on: September 24, 2015, 07:43:01 AM »

Do yourself a favour and ditch that exhaust and buy a propper tuned pipe,yes you can get a wrapto centre header or a wrap forward header its called a deep vee header,depending on room it could work for you.I use the wrap forward header that has a drop to it this puts the pipe down into the sponson.You can also use a drop down 90 deg header if you have the room length wise to accommodate the pipe this will give better power as it will tune better as the wrap forward headers tend to be a tad too long for optimum performance.Same goes for the  wrap to centre headers if you want the pipe to exit centraly.Actually the header you have is perfect if you want to exit centraly as it will tune betetr than a deep vee or wrap to centre header.Maybe see what Randy uses on his in the videos  and do similar.
Mart
Pipe id use nice and quiet and good power.

https://www.millpondmodels.co.uk/stainless-exhaust-with-muffler.html

if you want to exit pipe centrally through hatch at rear.

https://www.millpondmodels.co.uk/wtc-steel-header.html

this one could work in your hull as its a big cat should you wish to keep pipe inside and exit to the port side of transom

https://www.millpondmodels.co.uk/drop-down-header.html

you will need this also
https://www.millpondmodels.co.uk/zero-leak-flange.html
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #22 on: September 24, 2015, 08:23:30 AM »

Just noticed you have a water cooled flange so you dont need another   %) ,personally id stick with that header and just buy a nice tuned pipe,the one i linked is very quiet and under LEGAL deceble level unlike many so thats one less thing to worry about in case you have people who might not like noise  :} .
Mart
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BOATSANDBIKES

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Re: express craft 58" thundercat catamaran
« Reply #23 on: September 24, 2015, 03:11:38 PM »

thanks guys will use zx1 got a few pipes like one in link mart with cones inside muffler.think I will get your header as pipe will be off centre with one that's on now and at an angle
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martno1fan

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Re: express craft 58" thundercat catamaran
« Reply #24 on: September 25, 2015, 05:58:30 PM »

Maybe its the pic but it looks like it has the perfect angle to bring the pipe out centrally ?.
Mart
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