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Old 18-04-2017, 09:20 PM   #81
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Got out for a blast last night, weather was really nice, not warm though!
Engine is up at 70mm and revving a bit higher but roughly the same speed, 57.5 knots with myself and my girlfriend in it.
Went into a cave with it -


At the beach
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Old 04-05-2017, 06:06 PM   #82
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Was down at Easdale over the weekend at the Rib Rendezvous, had a really great time. Had an issue with the pull start before the event started, managed to get it fixed just in time on Saturday morning and caught up with the rest of the RIBs, over 30 the first day!
Covered over 90 nautical miles on the first day, plenty of chop so gave the boat a good run. Also some nice calm sections to go flat out, used around 80 lt of fuel - thirsty!






The thundercat was a very wet ride but a lot of fun!
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Old 14-05-2017, 07:18 PM   #83
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Boat and engine have been going really well lately, spent a lot of time cruising around here. Spent today fitting the primer kit in place of the chokes, haven't tried it yet but hopefully it should work well.


Should allow improved airflow as well, gives the air a clean channel down the carb throats


I also designed a new roller for the pull start, the old one was a bit worn!
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Old 11-07-2017, 05:24 PM   #84
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
So unfortunately looks like my photos can't be seen any more, photobucket wants $399 a year to host them... If I have time at some point I'll try upload them to a new site and edit all the posts

Recently changed the head on the Yamaha, removed the TSR one and found it was letting in water


so I've stuck the original head back on, performance seems about the same but waiting on some flat weather to get top speed figures. The old head isn't in great condition, if anyone has a spare 70ces head kicking about please give me a shout!


Also found that there was some flex in the transom, more than I'd like so I had another jack plate waterjet cut, 12.7mm thick so I could countersink bolts and have the plate flat against the transom which should reduce the flex. Also had some pull handles cut using the spare ali, these ones are a wee bit too big to fit through the cowling unfortunately so I'm having another made.


Tried the original 70hp carbs on, the engine just won't run properly with them, feels like it's running on 2 cylinders. I've rebuilt the carbs with new gaskets, cleaned the jets with carb cleaner and the airline and the jets are immaculate, so not sure what it could be. Also very hard to start with them, put the 90hp carbs back on and it starts easier and runs fine
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Old 19-07-2017, 05:15 PM   #85
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Had some excellent weather last week, got out for a spin and got some footage with the drone

https://www.facebook.com/seumas.macl...72511886123442
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Old 19-10-2017, 05:09 PM   #86
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Not got out in the boat so much lately, getting into winter now.
Had the original cylinder head reconditioned, looks really good. Interestingly the genuine Yamaha head gasket is around 1.4mm, the aftermarket one is 1.2mm so might increase the compression slightly.

Trying to get the engine to work with the standard carbs too, it just isn't happy with them, won't idle and it feels like it's dropping onto 2 cylinders. I've now had them put in an ultrasonic bath so I'll try them again. Designed another version of the throttle roller as it still wasn't getting WOT with the standard carbs. Unfortunately the roller broke when I twisted the throttle, so having another made in a harder material.

Looking at having the flywheel lightened too, not by much. The homologation sheet for the 70ces says 3800 grams so I'll take it to that, it will obviously be heavier due to the pull start attachment on the top. I'll have it balanced too, I suspect it's fairly well balanced from factory but won't hurt to have a finer tolerance



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Old 20-10-2017, 06:37 AM   #87
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Boat make: Hydrostream HST
Engines: Merc 2.5 200
Cruising area: The Schelde

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Cool project!
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Old 22-10-2017, 04:19 PM   #88
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Got the engine running yesterday and out for a run. Starts a lot easier now and runs smooth with the standard carbs and head which it hasn't done before. Throttle isn't opening fully yet - waiting for the new throttle roller to arrive.
New trailer arrived last night


Photo of some of my props


Did around 26nm yesterday, was nice weather but the throttle grip is still far too slippery so I removed the rubber section and designed a new one

hoping to have it 3D printed in ninjaflex which is pretty rubbery and flexible
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Old 04-11-2017, 09:39 PM   #89
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
3D print turned out really well, the grip feels really good. Very flexible too, just like the original rubber part but far grippier.



Got another throttle roller, made of resin so should be a lot stronger. The surface finish is completely smooth too, very nice piece


Bought this prop, was last used on an offshore racer with a Yamaha 60DES in the 80's. Looks sort of like a Hoss cut chopper, says 11x20 on it but measures closer to 10.5" diameter. Should go well on the Yamaha, possibly even better on the Tohatsu which seems to prefer overhub props
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Old 04-02-2018, 09:08 AM   #90
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Had the flywheel balanced over the winter, I assumed it would be pretty well balanced from the Yamaha factory. This is what I got:

"Your setup is 14.2 gm 25mm on the left plane. That creates a centrifugal force of 25.4kg at 8000rpm.
Taking it down to 2gm 25mm reduces centrifugal force to 3.5kg @ 8000rpm."


Got some new props, lots of testing to do

also looking at blueprinting the gearbox, maybe have the gears balanced like the flywheel. Might also go over the outside of the gearbox, make it more streamlined
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Old 12-02-2018, 02:05 PM   #91
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Country: United States
Location: Fort Myers Beach, Florida
Occupation: self employed
Interests: Boating fast
Boat name: Instant Insanity, Instant Insanity JR.
Boat make: Gemini Zapcat FF-15, Sunsation 24 rocket, 42 Outerlimits
Engines: Tohatsu 50hp TLDI, 530 cid 650 HP, Tripple 575 SCI Merc racing.
Cruising area: Southwest Florida and Michigan Great lakes

Join Date: Feb 2018
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I like your project

Can I ask what your motor you are running now and also on old boat. I read your measurements but can you tell me prop shaft center line compared to center line of hijacker center line?
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Old 12-02-2018, 06:37 PM   #92
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Hey, glad you're enjoying it!

Currently running a 2017 Ceasar F10 with a Yamaha 70ces. Before I had a Thundercat Inflatable with Tohatsu 50, then that hull with the 70ces.

Generally for 13-16" pitch props you want the centre of the prop shaft around 10mm below the bottom of the hijackers. Just run string across the bottom of the hijackers and measure from there, for bigger props like cleavers and choppers you might want to raise the engine up.
That's general setup, you can fine tune it depending on your crew weight, weather conditions, prop cup etc.
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Old 13-02-2018, 05:46 PM   #93
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
There's a new surfcat up here too, same guy who bought the thunderbolt. He's now sold the thunderbolt and bought this instead, brand new Yamaha 40hp 2 stroke on it.

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Old 14-02-2018, 06:26 PM   #94
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Country: United States
Location: Fort Myers Beach, Florida
Occupation: self employed
Interests: Boating fast
Boat name: Instant Insanity, Instant Insanity JR.
Boat make: Gemini Zapcat FF-15, Sunsation 24 rocket, 42 Outerlimits
Engines: Tohatsu 50hp TLDI, 530 cid 650 HP, Tripple 575 SCI Merc racing.
Cruising area: Southwest Florida and Michigan Great lakes

Join Date: Feb 2018
Location: Fort Myers Beach, Florida
Posts: 2
Thanks for the info, I guess I will have to cut my splash plate more because I am about 12 MM above the c/L of the hijackers.
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Old 19-02-2018, 07:15 PM   #95
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Who balanced the fly wheel and what did it cost
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Speed costs weight so what do we cut off first
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Old 20-02-2018, 10:59 AM   #96
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Was done by John Maher, he stays down in Harris so fairly local to me. He builds the best classic racing VW engines out there, really clever guy. Not sure if he wants more business doing the flywheels, we had to improvise a shaft to run in the balancer which wasn't perfect. Cost was £40
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Old 11-03-2018, 08:43 PM   #97
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Picked up a couple of Tohatsu 50hp's before Christmas, got them both running but both making a lot of noise due to worn crankshaft bearings. Tore one of them down so far, sent the crank off to have new bearings put on, ended up getting 1 new conrod too. Gave the pistons a clean, new base gasket, a lick of paint. Removed the lighting coils too, should free up a bit of power. Finally gave it a service, new plugs and changed gear oil. Tore the other engine down yesterday it will get the same treatment.





Also got another zapcat, from the same guy who sold me the Tohatsus. Looked pretty rough when I got it but holds air fairly well, just needs one patch. Gave it a bit of a clean today, going to have a look at removing some of the old stickers soon. Definitely needs a new floor, came with the old one but the ply is totally worn and coming apart.
Was thinking of doing up one of the engines up in matte white with custom stickers, then I'd have an all white boat to go with my all black Ceasar

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Old 12-03-2018, 07:58 PM   #98
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Get the cranks welded
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Old 13-03-2018, 09:29 AM   #99
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Quote:
Originally Posted by sinkunit0 View Post
Get the cranks welded
I asked for the crank to be welded, but when I spoke to them on the phone they said this one actually had a very strong press. Better not to have it welded if it doesn't need it, then if it needs new bearings in the future it's a lot easier to do
Sent the second crank away yesterday, I imagine this one will be welded
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Old 04-04-2018, 07:05 PM   #100
Thundercat guy
 
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Country: Scotland
Location: Isle of Lewis
Occupation: student
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 386
Was down in Stewartby last weekend, did a race in order to get a national racing license. Basically means I can attempt a British speed record at Coniston, exciting times! Got a few things I'd like to do to the boat before then, and lots of prop testing and tuning.
Racing was fun, was a circuit race first of the thundercat uk season. I jumped in the boat as codriver with Andy White (Team 55).

Even as codriver I get a driver license, so saved myself some money and the hassle of taking a boat down. Big thanks to Andy and the Haggis Hunter team
Also came away with a gold medal, chuffed with that!

There was an accident while we were dwon there, the driver was alright fortunately. Here's a link to the video -


Back at home now, had some nice parts waiting for me. New throttle roller I designed, 3D printed in Ninjaflex by a friend of mine, top quality part and has a ridge to stop my hand slipping


And some billet exhausts I designed for the 70ces, only keeping one of them. Really nice parts, top quality. Designed to homologation sheet dimensions but squared off a bit.


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