K90 KINGCRAFT in JAPAN

[Ian Inverarity]

Hammer,

3mm stainless should not bend!

Thanks for the CG info, I will check mine but I think it is slightly forward of that.

I saw your tank in one of the pic's and wasn't sure that it was a tank, but that is where I have mounted mine also. Mine is a 20 oz tank. I found this a very simple way to hold the tank in, and it is easy to see the fuel level. I have a 2 oz header on the other side strapped the the rail just in front of the carb.

Even with the tank close to the CG, I notice that the boat rides lighter as the tank empties.

K-90, make the second bolt a shear pin! That is what I do...

Ian.

 

[TimD]

K-90, make the second bolt a shear pin! That is what I do...

Ian.

Or maybe you could use a nylon screw for the second one. Easy to replace in a hurry.

 

[Ian Inverarity]

I use M3 brass screws as shear pins for all my fins and rudders. A little bit stronger than nylon, but will still give if I whack a bouy or go up the bank!

Ian.

 

[TimD]

Hey that can be my next excuse for buoy hits! "just testing the shear pins" ;D ;D ;D

Tim.

 

[Ian Inverarity]

Hey that's a good idea! And next time I flip my boat I will say I'm just testing the floatation and radio box seals!!! ;D

Ian.

 

[TimD]

Even better!!!! You win. 8)

 

[Hammerhead]

Hey Ian! I saw the shear pins on your turn fins. I think Dale is right. The mount for the turn fin needs a hair more surface than it has right now to accomadate the extra screw.

I lowered my pipe a lot. I went ahead and cut the body at the transom to do this. It seems to have illimimated the slight role it had when it peaked in the straights.

Gotta keep the weight as low as you can in the boat.

I have my engine so low, that I can barely get the starter belt under the flywheel.

Hammer

 

[Ian Inverarity]

Hammer,

If you look at the pictures of my boat and think about the turn fin brackets you will see that the brass screw takes no load in cornering, forces on it come from drag and hitting something only. By putting the fin on the inside of the bracket, the bracket and larger (M4) bolt at the top takes the cornering load.

My hardware is all home made,some of it works really well, but I am not sure the handling is quite as good as using the Kingcraft hardware.

I noticed you have lowered your pipe, this is a good idea as it also makes the pipe a little less vunerable in a crash. I also have most of my hardware etc pretty low, but you can go too far. If the CG is too low the boat won't lean into the corner very well, which badly affects the handling.

Ian.

 

[TimD]

Hammer san,

I am surprised to hear that you didn't try CF sheet for the turnfin - knowing your CF history with the riggers. Several layers of 6 oz. cloth compression moulded would be ultra stiff - then again something has to give and the fin is better for that than the transom. Maybe it's overkill. Stainless should be fine and will retain a razor sharp edge.

Tim.

 

[Ian Inverarity]

Hammer,

I checked my dry CG last night, it is 31.5-32cm from the transom, which confirms what I have long suspected, that is my CG is a bit far forward. It is a fair bit of work to move the CG back in my boat, so I am not sure when I will get to try it. I need to move the radio box and engine which means re-doing the stuffing box and all the radio linkages as well.

I have an X470/3 cut to 62mm to try now.

Ian.

 

[TimD]

Ian & hammer,

What are the RTR wieght lass fuel on both boats?

Ian you might be able to cheat a little and add some weight to shift the CG just to test your theory on the CG being too far forward.

Tim.

 

[Twin_k90]

Damm i need to get my new boat done,

 

[Ian Inverarity]

Tim,

I dont know what the weight is as my kitchen scales only goes to 4kg! I think it is about 5kg but I am not exactly sure. After the weekend I will take the engine out and weigh the hull, then the engine and see what I get.

To move the CG back by adding weight I would need a fair bit at the transom to do it, also I need to find a way to locate it. I think I can stuff lead sinkers into the floatation noodles, but that puts the weight fairly high too.

Ian.

 

[TimD]

Ian,

Is there any room between the transom and the radio box? Maybe you could attach lead weight to the rails near the transom??? I agree this is a band - aid method though. Moving the motor / radio would be the best and lightest way.

I thought of something else that might have an effect too - are you both running the same length trim tabs?

 

[Ian Inverarity]

Tim,

Dale (K-90) has suggested I fold up some lead sheet and screw it to the transom, which sounds like a good idea to me, keeps the weight in place and low! It would be a tempory measure to see if it stops the occasional stuffing I get. If it does, I can work on moving things later!

My hardware and radio box would be lighter than the stock Kingcraft gear so that has made the back end of my boat lighter than Hammers even tho our engines are in about the same position. Hence my forward CG!

My trim tab configuration is very different to Hammers, the outside tabs of mine are much larger! I am still unsure if my system is better or not.

Ian.

 

[Hammerhead]

Hey you guys! You are leaving me and Dale in the dust with this thread. Better do some catchin' up.

First of all, weight: With no fuel, I'm at 4.982kg.

I like the stock tabs, because you can adjust the inner side and the outer side independantly. They are very easy to adjust, they are tough, and they definately make a difference.

With my wave slave, I made the trim tab on the right with a larger surface. The right side, as you are looking at the transom, seems to have the largest effect due to the torque. But with the Kingcraft's independantly adjustable tabs, I can achieve the same effects. Not with surface area, but with shape.

Who ever designed those has made some heads turn over here. I wouldn't be suprised if I see some copies next season.

Hammer

 

[Ian Inverarity]

Hammer,

You and Dale must be getting slack!

Weight sounds about right!

My tabs are also split, they are different to those on the pics on Dale's site. I had tabs that were mixed to the steering so that they came up when the rudder was turned. This turned out to be a bad idea! It tended to flip the boat on the exit of corners as the speed was coming up and the rudder was still turned a bit!

I split the tabs, the inside tabs are still radio adjustable (I can re-trim the boat as it is going) but they are not mixed and the outside tabs are fixed. But my inside tabs are close to the keel, which may be casuing other problems for me...

Ian.

 

[TimD]

Come on Dale and Hammer,

We're leaving you in our wake!

The reason I mentioned tab length is because it will change the CG point. The lead sheet is a good idea to see if the CG point is the culprit. I was thinking of tyre weights myself but the sheet would be better.

Another thing worth comparing would also be transom to drive dog spacing.

Ian,

Dale tells me you have a Hummingbird Hydro - are you bringing it to the Nationals? I really want to see one of those things...

Tim.

 

[Hammerhead]

I came home for my lunch break today, and I made a stainless turn fin for the right side. I also was able to put a

shear pin in it. I used a 2.5mm aluminum bolt. It will break if I hit something. I use the same bolt in the rudders of my hydros. I have saved a lot of rudders using them. The rudder on my Hammerhead is spring loaded, so it doesn't need a shear pin. If I hit something, It will pop out, and spring back to the normal positition after the object is cleared. Works very nice.

Hammer

 

[Ian Inverarity]

Hammer,

Stainless should be strong enough!! The 2.5mm screw sounds like a good idea!

I have seen pics of your spring loaded rudders, looks like a good idea to me!!

Tim,

My inside tabs are shorter but the outside tabs are longer. I was trying out a personal theory on tab geometry. I am not sure if it is 100% successful yet.

My drive dog is probably about the same distance back from the transom, I based my hardware layout on the Kingcraft hardware. I asked John Finch about this exact point and he gave what he considered to be the optimum distance back from the transom, and it was pretty much what I was already running.

Yes I have a Hummingbird, yes I am bringing to the nats (A-90 powered). It is being painted at the moment, with luck I shall get it back this week and have it going a couple of weeks after that. It is the best built hydro I have seen, better even than the SG's. Even lighter too. I obviously haven't had it going yet, but so far I have to recommend them. Exquisite. Unfortunately it has taken me a long time to get it done, so I dont know how well it will be going for the nats. This is my first X hydro after all!!

Ian.