My Thundercat

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New Mako arrived a couple weeks ago, on the evening ferry on a Thursday then a hectic night getting it ready to leave first ferry on Friday. Weighed the old Ceasar which was a whopping 104kg. Mako is meant to be 77kg although not had a chance to weigh it yet. New Ceasar has arrived too so need to a do lot of testing soon.

Did 3 nights in Mallaig, got out to Eigg and Rhum with Douglas/Geoff W.

Up Loch Nevis another day, stunning area. Got to the Old Forge pub, most remote pub in mainland UK

No speed runs in the Mako yet but it's brilliant in the rough, handles the chop really well very comfortable and drier than any thundercat I've had previously

 

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Currently working out of Carradale, on nightshift so some time in the days to get out and about in the nice weather

 

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Ceasar arrived in October, still haven't been out in it. Very good looking boat though



Did some speed testing in the Mako in November, got upto around 57 knots but wasn't going flat out. Was half planning on returning to Coniston for records week 2023 but during the testing at home I was genuinely afraid. Never have been in a Thundercat before. Not the Makos fault I think I may just be done with trying to break records.
Going to keep my best props and things just in case I want to return to it later.

Also bought a 3.2m baby Thundercat, the idea being it can go on the roof of the car instead of a trailer. Will save a lot of money on fery travel, must have spent over £1000 on taking the boat to and from the mainland last year alone.
Got a nice 2021 Tohatsu 20hp four stroke to go on it, only 43kg. The boat itself is only 46kg.

 

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Made up some transom wheels for Piseag (gaelic for kitten, being a minicat), using a guide on Rib.net. Work very well, a bit tricky to do on a boat with an open transom but they fit


Got out for a spin on Loch Suainavat yesterday, a very deep freshwater loch just a few miles up the road. Boat goes alright, only the standard ali 10p prop on it at the moment but got a stainless 12p to test. Engine is very easy to live with, being 40 years more modern than my Yamaha 70ces and EFI which is nice!



Overall very happy, just need to make up proper roof bars to put the boat on the roof of the Subaru. Thinking a roofing ladder cut down to size so it has bunks like a thundercat trailer

 

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Stripped my Yamaha down again, the paint was really starting to fall apart. Going for powdercoat this time, in gloss black with some bits in red. Hopefully another carbon cowl in the works then maybe some custom graphics.

At powdercoating he found a crack in the swivel tube, just as well I got it done!
Crack welded up and a plate over the top of it. Need to get it all back together for Easdale

 

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Got the engine parts back last Wednesday, spent all day Thursday putting it back together then down to Harris on Thursday evening to get the morning ferry. Very last minute but made it!

Fantastic weekend down at ERR 2024, 110 nautical miles covered on Saturday. Thick fog on Sunday so didn't go out but got a great day on Monday round the South coast of Mull to Balfours Bay.
Thundercat performed absolutely faultlessly

Post from May 14th

 

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Despite having the dullest June on record got out a couple times



Can't believe it's 10 years since I started this thread

 

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Considering moving from the 70hp Yamaha down to a 50hp. Was even thinking of going to a four stroke, Tohatsu 50hp being the lightest.

Did a speed run or two towards the end of last year, only up to around 58 knots but felt real fear for the first time on the thundercat. Wasn't sketchy or anything just concerned about damaging my spine again. It still pops audibly 4/5 times a day when I stand up, not painful but it never used to do that pre Coniston '21.

Shame as I'd still love to hit 70 knots/80mph but I do feel I would need an active front wing in order to keep the boat stable at those speeds. I did continue developing it with help from a few folk but it's complex.

For now just happy using the boat for fun and various adventures, which is why I'm thinking of going to a 50hp. Haven't gone anywhere near full throttle with the 70hp for ages now. Also doesn't have tilt which would be handy, and having to remove the cowling to start the engine each time is a little annoying. I could change that but putting chokes back in the carbs but seems a shame to detune the engine which runs absolutely brilliantly.

 

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Couple shots from recent camping trips out in the boat. First photo is at Campay just north of Little Bernera. Can fit through that arch on a calm day.
Second night I wished I'd taken a bigger anchor, would've slept better for it




New engine, going to try it out on the old blue Ceasar to check it all works as it should. Will get the head skimmed at some point, but will be able to run regular 95 octane in this one. Yamaha 50hp 2 stroke, 1997. Not sure if I'll sell the 70 though, such a brilliant engine

 

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Got the 50 up and running. Had to machine an aluminium spacer and a plastic bush which were missing from the tiller assembly, made them up on a lathe.
Ran up alright but not perfect and took a lot of pulling. So pulled the carbs off and cleaned them, changed the fuel pump and cleaned out the filter. New set of plugs, started and ran better. Need to get her out on the water, have put it on the old blue cat for testing.

Will probably skim the head 1mm, need to do a squish test. The block is 6h4 which is 40hp, but the carbs look to be 50hp and the opening has been radiused with a dremel at some point so presumably ex race. Hoping it's still got the 50hp exhaust tuner, can't imagine anyone would bother changing that to a 40hp one when they changed powerhead.

Nice to have an engine that tilts up!

 

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Tried the 50 out today, unfortunately it runs terribly. Takes a lot of pulls to get going then cuts out in gear and won't take any throttle. Pretty sure there's some bearing noise coming from the crank too. Going to pull it apart and rebuild it, was probably going to do it this winter anyway so not too big a deal. Will do a couple of tweaks to get some better flow out of it but nothing drastic

 

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Pulled the Yamaha apart today, everything is in really nice condition no broken bolts or nasty surprises. Powerhead bolts were definitely not torqued, barely even tight in fact so opossibly an air leak there.
Bottom bearing on the crankshaft is a bit noisy so it was that I was hearing. The others fortunately are alright so that saved a chunk of change not requiring a crank rebuild. Pistons are 0.50mm oversize and the ports have been played with but look ok.

Made up earth wires for the coils, did this on my 70 and never had any issues with them since. Removed the temperature sensor and some other sensor from the cylinder head


Head before, taking it to get machined down don't know how much but so the beginning of the squish band is flush. I reckon it's around 1mm


Very very clean for a 1997 motor, even the paint is pretty good. I've put new control cables on already, old ones were split and rusty. Also new clamps for them, instead of the DIY bracket that was holding them on


I've ordered new decals for the cowling, the newer mid 2000's onwards style. Pretty sure the paint colour is the same or very similar so should look alright.



Was going to take the exhaust out and maybe modify it but the engine mount bolts are well stuck. Engine mounts look alright anyway so going to leave that all as is.

Also ordered a set of Boyesen carbon reeds, wasn't going to bother but don't want to do all this and then have a steel reed break and end up in a cylinder

 

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New stickers arrived for the cowling


Found a wire from the trigger coils to the CDI that wasn't connected which explains the poor running - only on 2 cylinders of the 3

 

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Got down to Taransay yesterday, a bit fresh on the way out F5 but had a fantastic time

 

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Started putting the 50hp back together, got a full powerhead gasket set from Yamaha along with a new bottom crank bearing and new crank oil seals.
Also put the new Boyesen reeds in. The wee screws that hold them on were too long even with the standard reeds so I used the dremel to make them flush. Reed blocks on the 40/50 are a bit of a choke point so more flow here is better. Can see before and after