Hydro pros..........need help, PLEASE!!

[Make-a-Wake]

Thanks Keith.......................i have a couple of straight turn fins..........i my slap one on just to see how she does without the cupping.

[domwilson]

To me it looks like a combination of issues. The strut may be a little to deep and as Darin suggested, the turn fin is pulling the sponson down. possibly because of the angle of the fin itself. You may want to angle forward slightly so the curve is parallel to the way the boat actually rides.

[Make-a-Wake]

Thanks guys.................just got back from a quick run..........no vid man with me, but she ran SO much better! Threw a fin on from a big mono.................she settled way down. At WOT she wanted to "hop" off the water a bit every now and then......not one sponson lifting, just the whole boat up off the surface at times. I ran it with a bit of positive angle............im going out when the batts recharge here in a bit and try it with neutral...................right?

PS - she turns better to the left...........

[dana]

Thanks guys.................just got back from a quick run..........no vid man with me, but she ran SO much better! Threw a fin on from a big mono.................she settled way down. At WOT she wanted to "hop" off the water a bit every now and then......not one sponson lifting, just the whole boat up off the surface at times. I ran it with a bit of positive angle............im going out when the batts recharge here in a bit and try it with neutral...................right?

PS - she turns better to the left...........

hey what a cool idea! now i want to try it with my ul-1

[Jesse J]

NOOOOOOOOOOOO, you took it off? Ahhh. ok, settling down (good wine at dinner). I am glad you have isolated the problem at the turn fin - at least you can replace that. it looked suspect the way it shook back and forth. Glad you took it off to test - my bad in telling you not too; I just have bad associations with when mine came off and she would NOT turn at all. Testing is a valid reason.

Cheers - well once you show us more vids -

wait... did you say she turns better to the LEFT??? What scale is this craft? and where did you put the turn fin? My buddy at the LHS keeps asking why we cant put two turn fins on hydros... tisk tisk.

I have hopping issues to solve myself. cupping the prop I was told.

still waiting for vids.

[Jesse J]

try it with neutral...................right?

Ideally you want a tad negative - 1 deg. this will keep the nose down when you are going mach 3.

[Make-a-Wake]

Hey Jesse, i used a straight fin as in the pic i posted above.............post #18. Its the standard 1/12 Elam.............28" or so.............

[Darin Jordan]

Ideally you want a tad negative - 1 deg. this will keep the nose down when you are going mach 3.

Just so you guys understand a little better... strut ANGLE mostly affects the BACK of the boat... lift increases as the angle increases at the back.

Strut HEIGHT affects the nose of the boat. The deeper the strut, the more it pushes the nose down.

Obviously the two aren't mutually exclusive, but in general, this is how it works...

[Make-a-Wake]

Thanks for the help Darin.................my strut is 3/4" below the hull bottom to the middle of the shaft..........its seems to be about where it would be stock..............i put an adj. strut on like you did. Little bit of Neg.........or neutral? I'll get some new vid when i can. Thanks again to everyone!

[Jesse J]

Just so you guys understand a little better... strut ANGLE mostly affects the BACK of the boat... lift increases as the angle increases at the back.

Strut HEIGHT affects the nose of the boat. The deeper the strut, the more it pushes the nose down.

Obviously the two aren't mutually exclusive, but in general, this is how it works...

Interesting, I was told the opposite. It makes more sense to me that the angle of strut, and therefore the angle of thrust, affects the force on the nose, whereas the depth of the prop, which wants to attain its surface penetrating position, will control the back of the boat.

This is the first time I have seen it stated to the contrary. Darin, why do you say this? have you some data to show that it is how you stated? I don't, other than my experience with trying to get my hydro to behave best possible. I have noticed that they generally behave as I stated, but am interested to hear why you have stated so decisively the opposite?

[Darin Jordan]

This is the first time I have seen it stated to the contrary. Darin, why do you say this? have you some data to show that it is how you stated?

Well... I may be remembering it backwards, but that's what Dick Crowe told me.

If you think about what angling the strut does (provides or reduces lift), WHAT is it "lifting"?? The BACK of the boat... When you leave the strut neutral, and move it down, it makes the back of the boat ride higher off the water, which forces the nose down.

Like I said, they aren't mutually exclusive, but in general, you push the strut down deeper in the water to help get the nose of the boat down, and you angle the strut more to get more lift at that back of the boat.

[Jesse J]

Well... I may be remembering it backwards, but that's what Dick Crowe told me.

If you think about what angling the strut does (provides or reduces lift), WHAT is it "lifting"?? The BACK of the boat... When you leave the strut neutral, and move it down, it makes the back of the boat ride higher off the water, which forces the nose down.

I am not convinced that simply lifting the rear of the boat does a whole lot to lower the front - it is being lifted as well by the air compressed under the tunnel. Whereas the angle of the strut will provide rotational force (stern to bow) around the center of mass axis running port to starboard, which will have more of an affect on the bow, and yes some but minimal affect on the stern.

Like I said, they aren't mutually exclusive, but in general, you push the strut down deeper in the water to help get the nose of the boat down, and you angle the strut more to get more lift at that back of the boat.

I agree that they are not mutually exclusive and it can be tricky finding a good combination, but I still think angle predominantly affects the front, depth the back. That said, I am very open to discuss the matter and am not in any way saying you are wrong - just not convinced.

for the record, I definitely do not consider myself a "hydro pro" just a modeler interested in learning how to better tune these dang hydros.

[Darin Jordan]

I am not convinced that simply lifting the rear of the boat does a whole lot to lower the front - it is being lifted as well by the air compressed under the tunnel. Whereas the angle of the strut will provide rotational force (stern to bow) around the center of mass axis running port to starboard, which will have more of an affect on the bow, and yes some but minimal affect on the stern.



I agree that they are not mutually exclusive and it can be tricky finding a good combination, but I still think angle predominantly affects the front, depth the back. That said, I am very open to discuss the matter and am not in any way saying you are wrong - just not convinced.

for the record, I definitely do not consider myself a "hydro pro" just a modeler interested in learning how to better tune these dang hydros.

It's possible I have it backwards. Your points on the thrust-line make sense. I tend to get stuff backwards when I try to remember it, and the more we "talk" this out, the more I question myself... NO WONDER I can't set a boat up!! However, when you raise the back of the boat, the front has to go down. On and OPC, for example, the outboard height will raise/lower the tips of the sponsons because it changes the height at which the rear of the boat wants to run. Angling the outdrive may appear to have a similar affect, but it's actually pushing up/down on the back, the same as lifting/delifting a prop... This WILL affect the nose of the boat. Both will/can....

[Jesse J]

Hydros are certainly my biggest challenge and why I have cats and monos to console myself. I respect anybody that works with hydros and KEEPS doing it. they can be incredibly frustrating and hard-headed (the hydros that is); sometimes they are downright naughty!!

But they are definitely the most sexy and romantic of the water crafts in my mind. There's nothing like the shear speed and ability to turn at that speed, plus that wall of water?? oooooh, just makes the hair on my neck stand up. They are the closest thing to an airplane with floats.

[MarkF]

Lifting the back of the boat up by lowering the strut can lift the hull up evenly or it can bary the nose. It all depends on were the cg is. This is used for getting the ride heighth were you want. When you angle the strut down ( negative) it tries to force the back up but also the front down. Good for boats that are tail heavy or flighty. Can cause hopping in hydros though. Pointing the strut up ( possitive ) will help hold the nose up. Good for nose heavy boats. Also helps monos hold the bow up in the turns and helps get rid of hop in hydros. This is my basic understanding of how the strut works. Of course every boat is different and you need to play with the different strut angles to tune your boat.

Mark

Mark