My thundercat - Page 30

Roflhat · 05 July 2022, 08:18

They must be running a lot of negative trim if that's the case, for me backing off the throttle always helps get the bow back down. The decelleration of the prop gives you drag at the stern almost like a brake. You can see at this angle the prop is pushing the bow up into the air instead of back down

Yeh that was my thoughts too, could almost go to the point where you run with the entire hull out of the water and just use the gearbox and the wheelie bar as the running surfaces like a reverse hydroplane. Would give a lot more stability with the prop ahead of the running surfaces.

It's pretty much the thing with cats, to get real speed you need to be right on the limit of stability as its the aerodynamics that give you the speed

Matt · 05 July 2022, 10:14

At that level, for sure. You're beyond the point of "driving" your way out of it. I'm talking about bow down, bombing along and as the bow just starts to rise. The big cat's get loads of lift off the props (same as the hydroplanes), so burying the throttle adds a bit of momentary stern lift.

What is your gearcase configuration? Have you looked at what the old Ocke Mannefeld Class 3 boats used to do - they ran very long gearcases - almost torpedo shaped - they benefited from stern lift for max speed.

I do however recall that a reverse 3 point hydroplane is meant to be faster, but less stable, than a traditional 3 pointer.
There's lots of discussion about it on the WSR chat groups - but you can see all the really fast stuff does stick with traditional 3-pointer config.

Matt · 05 July 2022, 10:39

Oh, the other thing you might find interesting - have a look at the rearwards running surface on the ocke boats, with it's concave shape. They do have a centre point - but that was a rules thing to ensure they were classified as monos and not cats - but I believe the concave running surface was pretty efficient.

Roflhat · 06 July 2022, 08:36

Standard gearbox but with LWP and nose cone added. Definitely helped, can feel when the boat sits up on the gearbox. I was wondering if extending the cavitation plate aft would help, almost double its length, so if the bow rises enough it catches the water and pushes the bow back down. A bit like the wheelie bar idea but the cav plate would only be one central one so less stable transversly, likely twist the boat in the air

Matt · 06 July 2022, 09:56

Depends how high you're running it.

Do have a look at what the C3 boats ran though - it was weird, but really seemed to work for them. It was nosecone+++++++.

Unfortunately I can't find a good picture to show you.

Matt · 06 July 2022, 10:07

Oh, here you go. Pattern Forme was a decent boat that IMVHO could have gone further, but made from wood and last I heard now rotton beyond repair.

Anyway, still a poor pic, but you can just about see the super long nose cone - way beyond any usual LWP etc.

Pattern Forme : Lorne Campbell Design

Roflhat · 07 July 2022, 07:51

Certainly is a long nose on that gearbox, I've seen photos of boats in Finland that have similar bullets.
Just sent Lorne an email, would be intersting to hear his thoughts on the thundercat

Matt · 07 July 2022, 08:04

Between the 2 - I'd be reaching out to Ocke. Lorne absolutely was decent and designed quite a number of old school cats, no criticism of his designs at all. But also, now, quite old "traditional". Modern cat designs have moved on a lot - much more lift, fully stepped etc.

The game changer was Ocke - his step & wing designs were a proper "step" change in hull design.

I think I asked before - I assume you have that tunnel hull design software that was knocking around a few years back? I think your design optimisation is already well beyond that anyway, but it was nevertheless interesting.

Roflhat · 07 July 2022, 08:28

Cool have sent them a message too.

I don't have that software, thought about it before and have spoken to Jim Russell. But as you say it's a bit dated, a friend of mine has it but its not all that useful for thundercats he says

Roflhat · 11 July 2022, 18:04

Didn't really get conclusive results with the CFD yet again, it's only a free online software though. But can see that the flat front on the cowling generates a lot of drag, going to try a rounded front again

Selling my current black Ceasar, plan is to buy a complete setup in Majorca. Then get another hull for back home, but no rush for it, want to get a well designed one I can keep going for records with

Matt · 11 July 2022, 18:10

Surely you’ve gotta be modelling you and your crew onboard too?

Crazy how the tech moves on. When I did my marine engineering degree CFD was the holy grail. Now you can do it for free, online.

Roflhat · 11 July 2022, 18:29

Was considering it but don't think so. Only looking to see the relative changes in design, don't need to get accurate numbers for drag and lift

Quite amazing that it's free, although the accuracy I'm not convinced by

Matt · 11 July 2022, 18:33

That’s fair. And only interested in some specific areas at a time too.

When I did my stuff a 486 DX2 66 on windows 3.1.1 was pretty state of the art. I’ve just ordered a “low” spec new PC with 12 threads, on 6 cores 4.4ghz, more ram than that old pc had disk, and a health 80TB of storage.

Roflhat · 01 August 2022, 16:42

Was down at the thundercat race in Plymouth last month, not taking part but got a zapcat to use for the day thanks to Jeremy Linford.

Back home for a week just now, entered a local rib race on Saturday. The navigation race was 18 miles, got spat out of the boat 5 minutes in. Choppy out there, did a jump we landed and the boat just hooked threw me out. Ian my copilot was hanging in by one ankle, looked pretty sore. Had to swim over and push him back in. Still carried on, tough racing a 10m rib with 500hp and a full suspension cabin. Came third in that challenge then 1st in the two handling sections which gave us 1st overall. Superb day out, don't have any photos just yet.

Today playing in the surf, tried launching from the beach which didn't work. Great fun again though, going to try use the boat as much as possible this week.
Put a deposit down on a zapcat in Palma already for if I ever get out there. But definitely going to buy one for home too, decided I can't be without!

Roflhat · 09 August 2022, 18:08

Placed an order for a new Ceasar F11, with a couple of custom touches. Nose cone is 40mm lower at the bottom on the F11 vs my pacemaker, and I've requested the transom to be lifted 20mm higher, the idea to have the deck at much less of an angle. 1.2 degrees vs 2.5 degrees overall so should be more stable at high speed. Bought an old Ceasar off surfer dude Mike who's bought my old pacemaker. Will be a stop gap until my new one arrives, hopefully in time for Coniston this year.
Gave her a quick clean tonight

Roflhat · 10 August 2022, 16:48

Did some more work on the boat today, tube polish, nose cone clean and polish. The port hijacker was leaking from the valve so I removed it and cleaned up the mounting surfaces.
Also sanded then painted the transom

Also found the bolts that hold the tiller onto the engine were slack, one snapped during removal so had a mission drilling and helicoiling that. Hopefully get the engine on tomorrow, weather at the weekend looks good

Roflhat · 25 August 2022, 08:48

Lots of boating action over the last week or two, weather not great but making the most of it anyway.

Having to sell my Subaru, needed a few things for an MOT then developed a misfire. Looking into getting a newer vehicle, 2015 onwards but don't know what yet. Needs to have enough room to sleep in, auto box, be able to tow and be able to launch on a rocky slope at the loch. Always used 4wd for that but might manage with 2wd and chunkier tires. Considering a Passat Alltrack or Ford Transit Custom

Roflhat · 13 September 2022, 17:11

Decent weather the last week or so, plenty of thundercatting to be done

Some more progress on the front wing, new board and sensor and the code is working perfectly. Need to sort out a battery setup still but looks promising.

Considering getting the new thundercat made in TPU, but very light stuff 730g/m2 compared to PVC Valmex at 1000g/m2. Potentially save upto 10/15kg, it's a risk but TPU is tougher than PVC and my boats generally don't see a lot of abrasion

Roflhat · 18 October 2022, 12:42

Got the wing tested today, pretty happy with how it performs. Need to tweak the output angles but it survived upto 50 knots at least!
http://youtu.be/zTql3nddrnA

Redkelly · 01 December 2022, 19:22

Quote:

Originally Posted by Roflhat

That's a bad example

45mph is pretty slow. The zapcats arent as fast as thundercats though, they're too heavy.
Our jetski is a big 3 seater yamaha, great machine but very uncomfrtable in really big waves like we get up here, thundercat can go through just about anything.

Hi im new to all this and have been scanning the internet for the right information and so far i found people saying they arnt very good in big swell and now someone say (you) saying they can handle pretty much anything, which alines with my original thoughts with thundercats as they were made for surf raceing it makes sense in my mind.

So i was hoping you could go into more detail about what you have taken your thundercat through and or seen them handle.

A little background around what i want one for.

Where i live in australia via water it takes 20 min to get to work but i have to cross open see going out through what we call the heads. Which can get large ground swell and breaking waves in the right conditions. Which most of of the time i will avoid those days but you cant plan for every thing and i wouldnt want to get stuck out there in a boat that cant get me out trouble if it neads to.

Thoughts

Thanks