Effects of extended struts on Hydros .

[dwilfong]

lots of curves and angles looks KOOL.
But it just adds more variables in to the mix that are not needed to make a rigger perform good.
If there are to many things controlling the boats attitude it becomes a hand full to set up.
Thy start fighting them self and you never find a good balance.
In race water there is no rime or reason to the water.
Fell in enough holes in the water to under stand that.
A boat needs to be able to recover from a bad pop up or drop in when racing.
Balance is every thing.
Angles will gust exaggerate any abrupt change in attitude.
K.I.S.S.

 

[dr gary turner]

I ask Jim Wilson one time If i put a longer strut on my sport 20 will the boat thinking it will trick the boat being longer and Jim's reply was NO.

Dave it affects the after plane

 

[DON MAHER]

In regards to afterplane, the true measurement is from the heel of the sponsons to the prop! Moving the prop forward or back will also effect the tail weight and c/g of any style hull !

 

[dwilfong]

Do me a favor and measure your tail weight at the prop tip.
Then move the prop back with just the shaft 1.5" and do it again.
Tell me what you find.

 

[ALLAN YUEN]

See picture of Danny K ‘SGX90 high speed

 

[dwilfong]

See picture of Danny K ‘SGX90 high speed

That is one split second in time.

 

[Wasted wages]

Lots going on in that one second.....

 

[Wasted wages]

At 21,000 rpm.... that prop has made 350 revolutions in that one second.

doesn't seem possible, does it...

 

[Steve White]

It would be great to see a series of shots, 2-3 frames per foot of travel showing the sponsons & prop to see the dynamics of boat in motion.

 

[Kez]

See picture of Danny K ‘SGX90 high speed

Going a little off topic here... but the picture showed that the cable does not shrink in length under load. I leave a 1/16" gap in the cable. Most would consider that gap to be too small. But the thrust washer has no wear mark indicating the does not shrink under load.

kez

 

[Terry Keeley]

A good turning 21 will run 30K+, that's 500 revs/sec.

A two bladed prop will dip into the water 1000 times/second! So every 0.001 second a blade hits the water.

Incredible.

 

[John Finch]

When I was running nitro in 1982 I used an extended strut to set an oval record on my mono because it reduced prop walk because water was able to hit the top half of the prop as well as the bottom half in relation to the hub being the center of rotation. I published that finding and slowly it caught on. I am not saying I invented the extended strut because there is always someone out there who has done something before anyone else, but I did promote it. On an outrigger with the prop hub out of the water the extended strut may not be an advantage for prop walk in clean glassy water because the prop above the hub is out of the water, but how does the transom sit in the water while cornering or in rough water. Do the waves hit the prop blade that is above the hub? Certainly does. For SAW I run a strut with no extension behind it because I want the prop area above the hub to aerate the prop on launch so I can swing a larger prop, but for heat racing I want to extend the strut for better propwalk control. As far as reducing propwalk I have ALWAYS found that the leverage of the rudder is key. At 100 mph only a small rudder is needed to keep the boat straight with a huge prop because the water pressure is so strong, but for heat racing speeds a larger rudder is needed. Speed can dictate rudder size. More importantly, where the rudder is mounted in relation to the prop can make all the difference in the world. On some riggers the rudder can be mounted closer to the transom than the prop, but with riggers that have propwalk problems putting the rudder further back from the transom than the prop will create more leverage to prevent the prop from dragging the transon to the left. A rudder behind the prop and to the right will allow a turn fin run parallel to the tub for better control than using toe in on the turn fin. Toe in on the turn fin makes the boat crab down the straights. Most of what I read here is correct about rudder tilt, recurve, extended struts etc. I have done extensive testing on all those things. But like Doc said it all depends on the boat design and purpose for the boat. So many things are interconnected with struts, turn fins, cg, prop design, pitch angles etc. that there is no one setup rule for all boats. I miss the communications I used to get with the nitro boaters now that I run all gas boats. You guys know the why more so than most and I probably didn't say anything you didn't already know but it was a good read for me.

John

 

[Steve White]

^^^ Excellent summary John and thanks for sharing your vast experience on this topic. I've also noticed that hydroplane prop walk is relative to power output of the engine - at least with the boats I've ran. More power and it's easier to get them to track straight - maybe that's simply what you alluded to on speed -vs- rudder area.

I started something years ago with regard to props. I don't run what I call "magic props", just run stock over-the-counter props that are cleaned up, balanced and polished. Tune the setup around stock props - then when one gets torn up, just grab a spare. Could be losing out on huge performance gains - but, it's happened that the "magic prop" got wasted on race day and no replacement in the parts box - and boat performance suffered as a result. Consistency is important, reliability as well - gotta get through it all and cross the finish line to have a chance of winning anything.

 

[Ray Sametz]

^^^ Excellent summary John and thanks for sharing your vast experience on this topic. I've also noticed that hydroplane prop walk is relative to power output of the engine - at least with the boats I've ran. More power and it's easier to get them to track straight - maybe that's simply what you alluded to on speed -vs- rudder area.

I started something years ago with regard to props. I don't run what I call "magic props", just run stock over-the-counter props that are cleaned up, balanced and polished. Tune the setup around stock props - then when one gets torn up, just grab a spare. Could be losing out on huge performance gains - but, it's happened that the "magic prop" got wasted on race day and no replacement in the parts box - and boat performance suffered as a result. Consistency is important, reliability as well - gotta get through it all and cross the finish line to have a chance of winning anything.

Like my signature says, 0-DNF'=Wood....or trophy.

 

[Steve White]

^^^^ "Wood" is good!

 

[Tom Foley]

Going a little off topic here... but the picture showed that the cable does not shrink in length under load. I leave a 1/16" gap in the cable. Most would consider that gap to be too small. But the thrust washer has no wear mark indicating the does not shrink under load.

kez

What is everyones point with these thrust washers in a standard cable , collet , thrust into engine setup ? Just leave it out it's worthless !!