Avon unstable at speed - Page 5

A1an · 28 March 2013, 22:01

Quote:

Originally Posted by teamplonker

I'm thinking the weight difference between the two is a big factor, Ive only ever had 2 strokes before and am aware that they are lighter.
I just went for a 4 stroke as i thought it would be more reliable and better on fuel.
I'm not sure it was the right decision now

Yep, like I said earlier the Honda is a big lump but I don't know if it would make vast difference.

What prop are you running?

teamplonker · 28 March 2013, 22:31

Quote:

Originally Posted by A1an

Yep, like I said earlier the Honda is a big lump but I don't know if it would make vast difference.

What prop are you running?

Its a genuine Honda ally 18.5 x 15, Jock gave me a brand new spare as well but i think its the same size.

Rogue Wave · 28 March 2013, 23:21

latest honda 75 weight - 163kg

latest Suzi 90 - 150kg

yammi 90 2 stroke - 122kg

Optimal speed doesn't usualy 't come with low power to weight ratios so i think I think thats good speed your getting.

Also doesn't a four stroke bang on every other stroke and a 2 stroke every stroke I have always felt the power was a little more immediate and smellier and noisier and betterer.

Having said all that I really am impressed bu our Yammies f70 power to weight and sdtunning fuel economy and I'm hearing there is a lightweight F90 out soon

teamplonker · 28 March 2013, 23:41

Quote:

Originally Posted by Rogue Wave

latest honda 75 weight - 163kg

latest Suzi 90 - 150kg

yammi 90 2 stroke - 122kg

Optimal speed doesn't usualy 't come with low power to weight ratios so i think I think thats good speed your getting.

Also doesn't a four stroke bang on every other stroke and a 2 stroke every stroke I have always felt the power was a little more immediate and smellier and noisier and betterer.

Having said all that I really am impressed bu our Yammies f70 power to weight and sdtunning fuel economy and I'm hearing there is a lightweight F90 out soon

Just been looking at the price of some yamaha 90s on ebay priced from about £2000 - £2500. If I keep this boat I may do the engine change not just for speed but stability too, all that extra weight is obviously no good.
And i'll have to see how much i can get for the Honda.

matt h · 28 March 2013, 23:49

That lump look soooo heavy. used to get 38 -42 with a Yam 90 13 1/4 x 19 pitch standard prop and 50 litres of fuel single up.

teamplonker · 28 March 2013, 23:50

Quote:

Originally Posted by teamplonker

I had a word with the Harbour masters first and asked nicely if i could test the boat in the basin.
Eat a little humble pie give a big smile and hope for the best, this usually works. Ive been testing my boats down there since the early 90's, if your sensible they don't mind.

Avon Searider 5.4m Rib - YouTube

matt h · 28 March 2013, 23:59

Looks pretty balanced given the waves and small testing ground but its doesnt looks exciting and just looks heavy..were you full throttle at all? Flog the Hongdu and Get a yam 90, it will transform it! there would be 57 kgs difference hanging off the back and for a 2-0 mtr beam boat thats all the difference

teamplonker · 29 March 2013, 00:03

Quote:

Originally Posted by matt h

That lump look soooo heavy. used to get 38 -42 with a Yam 90 13 1/4 x 19 pitch standard prop and 50 litres of fuel single up.

I may have a look at different props, but the rev counter is not accurate so i'll need a new one before i go messing around.

Do you still have your boat with that set up ?

teamplonker · 29 March 2013, 00:12

Quote:

Originally Posted by matt h

Looks pretty balanced given the waves and small testing ground but its doesnt looks exciting and just looks heavy..were you full throttle at all? Flog the Hongdu and Get a yam 90, it will transform it! there would be 57 kgs difference hanging off the back and for a 2-0 mtr beam boat thats all the difference

No thats not full throttle on the vid that was my youngest getting used to it,He was only doing about 20 - 25 mph.
He's still a bit nervious on it too as he was with me when it started chine walking.

Rogue Wave · 29 March 2013, 02:02

Hndas are quite popular engines with the fishing boys put it up on find a fishing boat and see if you get any bites

Chris · 29 March 2013, 08:25

Have you lifted the engine on the transom yet. In the first pics it looked way too low ad this would hamper your performance.

Also it would be worth checking the engine over to make sure the throttle is fully opened at WOT. As over time cables stretch and setting need tweaking...

I agree that a 90 2 stroke will be great however you might be able to wring a little more out of the Honda.

teamplonker · 29 March 2013, 09:31

Quote:

Originally Posted by Chris

Have you lifted the engine on the transom yet. In the first pics it looked way too low ad this would hamper your performance.

Also it would be worth checking the engine over to make sure the throttle is fully opened at WOT. As over time cables stretch and setting need tweaking...

I agree that a 90 2 stroke will be great however you might be able to wring a little more out of the Honda.

Haven't raised the engine yet, thought i would move the consoles first.
I'm a little hesitant to lifting the engine as worried about stability.

As for squeezing a few more horses from the engine I think i may take it up to samspeed marine in glou for a dyno tune if its not too expensive now, they tune the boat in a tank.

Probably best to save the money and put towards a Yamuna 90

Rogue Wave · 29 March 2013, 10:46

Quote:

Originally Posted by Chris

I agree that a 90 2 stroke will be great however you might be able to wring a little more out of the Honda.

good point run it on Nitro

C-NUMB · 29 March 2013, 13:45

Quote:

Originally Posted by C-NUMB

Can't swear my engine is totally in center(need to check) but have a vague memory that previous owner moved the engine from offset to centre of transom, so not so sure that is the issue, as it works fine on this boat.

At least I would not start with moving the engine sideways at this stage. But would try another propeller and also playing with weights also sideways. My console is offset to starboard.

I just measured for checking. Engine in my boat is in center of transom, spot on.

Here a video of mine set-up

SR 5.4 and drift hd 170 .avi - YouTube

Skip it until 7:09 , there it is doing about 39.5 knots. Boat has Teleflex steering having some play as usual. Boat was little stern heavily loaded this time.

I am convinced that one can get a SR to handle OK with a 175 kg lump. If knowing the location of LCG with the 90 Yam, then moving the battery, tank and maybe console to obtain the same LCG with the heavier engine, handling should not be that much different? Total weight (affecting performance) will be higher though. Another option is to move a 20 kg led weight, guess putting that in the bow would already pretty much keep the LCG in same position.

I love the Yam 90, but it is little noisy....wonder how is it compared to the sound of a 90 optimax?

teamplonker · 29 March 2013, 17:31

Just had another look at the outboard height and the cavitation plate is probably an inch below the boat so i think i should bring it up a notch and make it level.

teamplonker · 29 March 2013, 17:36

Is this Too low, I have always thought cavitation plate should be level with bottom of hull

matt h · 29 March 2013, 18:36

bring it up one hole

teamplonker · 29 March 2013, 19:47

Up one hole, I think it could go one more.

Nos4r2 · 29 March 2013, 22:15

It looks better.Try it first.

benjytaylor · 30 March 2013, 17:41

Quote:

Originally Posted by teamplonker

Up one hole, I think it could go one more.

That will be much better. Try adding some weight to the bow also. Poss sandbags to start. I had to do this to one of my seariders then eventually grp 40kg into the bow locker. Works a treat and still gets 34kts. Good luck