05-20-2009, 09:26 AM #1
What hull angle is ideal? (wedges, angled plates, different nozzles, so many choices)
By using different combinations of handling parts we can alter
1) the angle the ski rides in the water
2) the willingness for the ski to bounce up and down or porpoise
3) the ski's ability to corner
If you raise the hull angle, by that I mean, if you raise the front of the ski higher in the water you will
1) go faster if the water is flat enough for the hull angle you are trying to use (this is true until a certain point is reached and then speeds will decrease)
2) increase the ski’s willingness to porpoise
3) reduce the sideways grip of the hull in the water (the keel and the chines have less grip). This means the ski will slide more when cornering hard.
To increase the hull angle you can
1) increase the rideplate angle
2) increase the exit nozzle angle by either using a nozzle with more angle or using a pump wedge
3) lower the trim tab height
4) trim up on the ski
5) move more weight to the rear
6) have less fuel in the tank
To lower the hull angle in the water you would simply do the opposite of the above.
So now the trick becomes finding the best combination of parts and the proper set-up for the conditions you are riding in.
If you ride in an inner channel waterway where the water is flat as can be then getting the front end up as much as possible will provide the best results. Just look at the recent excellent results Team Florida is getting with the hull riding higher than most people thought was possible. Though this approach is proving to be very difficult to copy as illustrated by the fact nobody running in the 80s or 90s at MB was using a wedge.
But if you ride in rough water conditions the opposite condition exists, you want the front to be planted down in the water.
One on our forum members is Billy Dearman and he races GPRs closed course and is typically racing in extreme conditions. I spoke with him at one of his races last year. He was racing on Lake Ontario and the water conditions that day were especially rough. Even though his ski set-up was using an aftermarket “0” degree pump nozzle and aftermarket extended trim tabs he told me he ran the entire race with his mechanical trim tabs in the down position. This was the only way he could keep his ski from bouncing up in the air off the waves.
In Billy’s case he was able to maximize his top speed in the rough water conditions, not by raising the hull up in the water, but by doing the exact opposite. Instead he lowered the front end in the water. ( and yes Billy had a good day, it was nice to see the GPR on top )
To try and answer the question, what effect adding a pump wedge will have on a specific ski, you have to consider 3 things
1) the inherent ride characteristics of that ski model
2) what set-up is being used on that ski
3) what the water conditions are
Let's review each of these points individually
For example, if you compare Yamaha 2 stroke skis to the newer 4 strokes you see they are very different skis. The GPR and XL are lighter, have different hulls and they both tend to ride more front end light. This is especially true of the GPR.
The XL comes from the factory with a 3 degree nozzle. The GPR and FZR come from Yamaha with a 5 degree nozzle.
Common ski set-ups
The XL ski responds easily to ski mods that focus on getting the hull out of the water more to raise top speed. People have been adding the 5 degree GPR nozzle to the XL for years now. The GPR responds even more, primarily because you can use the trim tab settings to help stabilize the hull. In both cases there is a sweet spot that the tuner strives for. You can maximize the top speed of the ski by using the right combination of parts etc to get the hull riding in the water at the optimum angle. If we don't have enough hull angle the ski will be slower because of additional drag. Likewise, if we have too much angle we can also create a condition where we are also increasing the drag and / or creating a condition where the hull isn't stable in the water.
The FZR (so far) is not providing the same degree of top speed gains by these types of handling mods. Simply stated, it doesn't respond as well when you try and get the hull out of the water. Efforts in this direction often lead to the ski hopping. The FZR (and SHO) are new skis so this is still work in process. It should be also noted with the potential for the 4 stroke motor to make huge HP this adds another dimension to this discussion. The more HP you have the faster you go. The faster you go the more lift you will get from the hull.
Finally as discussed in Part 1, CC racers are able to raise their average top speed in rough water by lowering the front end down (and not raising it up.)
So the job of the tuner is to find the right combination of parts and settings that result in the ski riding at its optimum hull angle for the water conditions being ridden on. This is very much a balancing act. If too little angle is used the ride quality typically improves, but top speed is lowered. If too much angle is used top speed is also lowered but in this case the ride quality will deteriorate dramatically.
Part 3 - So you want the ski to corner harder (or you want to race closed course)
Hull Angle and it’s effect on cornering
By using different combinations of handling parts we can alter the ski's ability to corner.
If we want the ski to be able to corner harder then we want to use a set-up with the appropriate parts that will give the hull more grip in the corners.
Let us consider what effect the angle the hull rides in the water on cornering. If you raise the hull angle, by that I mean, if you raise the front of the ski higher in the water you will reduce the sideways grip of the hull in the water (the keel and the chines have less grip). This means the ski will slide more when cornering hard.
Likewise, to lower the hull angle in the water in order to improve cornering you could:
1) lower the rideplate angle
2) lower the exit nozzle angle by either using a nozzle with less angle or using a negative degree pump wedge
3) increasing the shims under the trim tabs
4) trim down on the ski
5) move more weight to the front
6) have more fuel in the tank
Auto-drop (steering) Nozzle
An auto-drop nozzle automatically lowers the steering nozzle trim when cornering. This lowers the front of the hull in the water to give it more bite.
The current trend for the OEM manufacturers is to provide sponson's where their primary design objective is to provide hull lift and not cornering grip. This has provided an opportunity for the aftermarket manufacturers to offer sponson's designed to improve a ski’s cornering ability.
For most skis the OEM rideplate actually does a very good job of keeping the ski planted in the water when cornering hard. The aftermarket rideplates are often designed to raise the front of the ski up out of the water in order to raise top speed. As described above this has a detrimental effect on cornering.
In order to improve acceleration of the ski when exiting out of a corner you can do the following:
1) seal pump area properly with a pump plug kit and the proper sealant
2) use an aftermarket top loader intake grate
3) typically any aftermarket impeller will do a better job than the OEM impeller, the best designed impeller for acceleration is a Skat trak full swirl impeller
4) increase horsepower
Last edited by philip_gpr; 05-08-2010 at 09:14 AM.
05-20-2009, 09:38 AM #2
Mods need to make this a sticky for the new guys
05-20-2009, 10:12 AM #3
Good post.. Has anyone tried this combination by putting the battery in the front of the compartment to alter the weight distribution?
Yes people will say you might loose top end in flat water.. but does it help keep you in rough water along with trimming it down?
Does the reward make sense in this case?
I know people say set your ski up for flat or rough blah blah haha. but There has to be a pretty sweet combo for both meaning like if your ski is setup for +5 mph gain on flat and crap on rough maybe only +2 better... Then is there a trick? Combo? Battery placement? Nozzle adjusted? That allows maybe +4 flat water gain and +3.5 gain in rough?
Hopefully this is a valid questions?
05-20-2009, 10:21 AM #4
yes I agree with what you are saying, from the stand point you don't have to have your ski set-up at one extreme or the other extreme
you can set it anywhere between the 2 to get the best compromise for the conditions you are riding in - for example the Shred Master rideplate is a compromise rideplate - it only provides a 1 mph speed gain (sometime not even that) but it handles great in the rough water
Yamaha tries to provide some flexibility with the manual trim - with all the other parts we now have available we have all sorts of choices
On your battery location question, I personally don't like the front end heavy feeling the ski has when it has a full tank of gas so my ski I have gone in the other direction and tried moving weight to the rear.
05-20-2009, 10:32 AM #5
So do you bounce more than usual then at top end with the littliest of wake?
05-20-2009, 10:32 AM #6
Do you bounce more on the tinniest of wake on top end?
05-20-2009, 11:03 AM #7
My ski is setup for choppy conditions and there is nothing better than flying across the chop when others can't stay hooked up and are left behind.
Flat water is fun but, most of the time it's never flat. Set it up to run in the average conditions you ride in, and not top speed. If you set your ski up for top speed you will be disappointed most of the time.
My ski could run into the 80's all loosie goosie, but average riding conditions I will get beat every time. But when I have it setup to run 76-77 I own our waters..
05-20-2009, 11:16 AM #8
Do you mind laying the details out of your ski for both conditions?
05-20-2009, 01:20 PM #9
05-20-2009, 02:45 PM #10
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