What makes a good rough water hydro?
- Thread starter TimD
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Chris Attebery
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- Jan 13, 2003
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Tim,
I have had a few hydros and have been able to set them up fairly well for the rough stuff.
Here are my suggestions:
1. Start with a decent size hull, it doesn't have to be huge, but at least average size. The bigger the footprint the more stable the hull will be.
2. Set the front sponsons up so they have 3.5 to 4.0 degrees of attack angle. This will keep the front from stuffing.
3. Use a strut/prop combo that holds the front down. I used lifting props and 1-2 degrees of negitive angle. This will allow you to use the steeper sponson angles.
4. A heavier hull will fair better in the rough.
5. Use a prop that is one to two sizes smaller than you normally run so you can stay on the throttle and keep the motor warm.
6. A well sealed engine compartment. One drop of water int he carb when you're off the throttle can kill the motor.
That's all I've got. I'd love to hear anyone elses suggestions,
Chris
I have had a few hydros and have been able to set them up fairly well for the rough stuff.
Here are my suggestions:
1. Start with a decent size hull, it doesn't have to be huge, but at least average size. The bigger the footprint the more stable the hull will be.
2. Set the front sponsons up so they have 3.5 to 4.0 degrees of attack angle. This will keep the front from stuffing.
3. Use a strut/prop combo that holds the front down. I used lifting props and 1-2 degrees of negitive angle. This will allow you to use the steeper sponson angles.
4. A heavier hull will fair better in the rough.
5. Use a prop that is one to two sizes smaller than you normally run so you can stay on the throttle and keep the motor warm.
6. A well sealed engine compartment. One drop of water int he carb when you're off the throttle can kill the motor.
That's all I've got. I'd love to hear anyone elses suggestions,
Chris
ClayGlover
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- Oct 23, 2002
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- 932
chris- when you say 3.5 to 4.0 degrees of attack angle, do you mean the bottom rearmost portion of the front sponsons in reference to a flat table with the hull being level?
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- Nov 2, 2002
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From my Cobra/Stinger days, boats that bounce flat! These designs in rough water would bounce off the water staying horizontal. I have seen some other designs that tend to 'kite' in rough water, they bounce the front up a lot more than the rear.
One of John Finch's books suggested that this was due to the aerodynamics of the boat being balanced such that they did not casue the boat to pitch up or down in flight. I think this is definately a factor.
But I wonder if this pitching up at the front is more to do with the relative sponson areas of the front and rear, and also the CG placement. Both the Cobra's and Stingers have quite large rear sponsons and run a CG comparatively forward. Other designs I have seen that seem to pitch up in rough water have relatively small rear sponsons and a more rearward CG.
On the other hand, looking at the pics of Hammer's friend's boats, these have a very rearward CG and often no rear sponsons, yet are supposed to be very good in the rough??? :-
Does anyone have formulas for calculating sponson areas? Ie if a sponson riding surface is at 3.5 degrees, you have a rough idea of the predicted speed and weight of the boat, how wide does the riding surface need to be?
Ian.
One of John Finch's books suggested that this was due to the aerodynamics of the boat being balanced such that they did not casue the boat to pitch up or down in flight. I think this is definately a factor.
But I wonder if this pitching up at the front is more to do with the relative sponson areas of the front and rear, and also the CG placement. Both the Cobra's and Stingers have quite large rear sponsons and run a CG comparatively forward. Other designs I have seen that seem to pitch up in rough water have relatively small rear sponsons and a more rearward CG.
On the other hand, looking at the pics of Hammer's friend's boats, these have a very rearward CG and often no rear sponsons, yet are supposed to be very good in the rough??? :-
Does anyone have formulas for calculating sponson areas? Ie if a sponson riding surface is at 3.5 degrees, you have a rough idea of the predicted speed and weight of the boat, how wide does the riding surface need to be?
Ian.
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Hey Hammer,
I see from the Japanese site there is a bit of a construction article for a red and yellow 90 rigger. I cant read it, but the pics show plans. Are these plans available? If not, do you know the specs of this boat? Like weight, riding surface width, afterplane, sponson track width etc?
Ian.
I see from the Japanese site there is a bit of a construction article for a red and yellow 90 rigger. I cant read it, but the pics show plans. Are these plans available? If not, do you know the specs of this boat? Like weight, riding surface width, afterplane, sponson track width etc?
Ian.
MikeP
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- Mar 13, 2002
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I used mostly JapanHammer design on my hydros, I do not know why but it works extreamly well in rough water, most notable is it jumps and flies level. That makes it reliable in the rough. My .21 and .84 have never blown over or stuffed. I am not an engineer or experinced hydro builder just been very LUCKY!
-MikeP
-MikeP
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Mike,
Your boat uses long rear sponsons doesnt it?
What is the afterplane, sponson track width, riding surface width? (if you dont mind saying of course! ;D ) What about CG position?
Ian.
Your boat uses long rear sponsons doesnt it?
What is the afterplane, sponson track width, riding surface width? (if you dont mind saying of course! ;D ) What about CG position?
Ian.
MikeP
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Here are some measurements.
Rear sponsons
15" long 1.5 deg. AOA .5" ride surface at the rear.
www.ad.kengarff.com/mikep/cf90/rearspon.jpg
Front sponsons
2.125" ride surface, 4.5 deg. AOA, track width 14.125 inside edges.
After plane 28"
CG 80% of afterplane, empty fuel cell.
turn fin centered on CG
I have made several rear sponsons and attached them on with double stick tape. The rear sponsons have the biggest effect on the handling of the boat. When there set right everything is good.
I played with some other adjustments to see what would happen, wider front track width and the front sponson AOA and didn't notice much difference.
Hope some of this helps.
-MikeP
Rear sponsons
15" long 1.5 deg. AOA .5" ride surface at the rear.
www.ad.kengarff.com/mikep/cf90/rearspon.jpg
Front sponsons
2.125" ride surface, 4.5 deg. AOA, track width 14.125 inside edges.
After plane 28"
CG 80% of afterplane, empty fuel cell.
turn fin centered on CG
I have made several rear sponsons and attached them on with double stick tape. The rear sponsons have the biggest effect on the handling of the boat. When there set right everything is good.
I played with some other adjustments to see what would happen, wider front track width and the front sponson AOA and didn't notice much difference.
Hope some of this helps.
-MikeP
- Joined
- Nov 2, 2002
- Messages
- 2,662
Thanks for the info Mike! ;D 8)
Both of your front and rear riding surfaces are considerably narrower than on my 90 Hummingbird. :-
Why do you think the boats blew off? Did they lift off at the front and flip like a typical mono or cat? Was the water very rough?
Ian.
Both of your front and rear riding surfaces are considerably narrower than on my 90 Hummingbird. :-
Why do you think the boats blew off? Did they lift off at the front and flip like a typical mono or cat? Was the water very rough?
Ian.
