In depth - Prop depth question? (punn intended)
 

I can definately see how propshaft depth in relationship to the bottom of the boat, or other parts of the running surface of the boat (like our stepped transoms), could have an effect on prop bite or slip. This measurement can be measured in a variety of different ways.

Question: How do you think boat weight plays a part in prop depth in relation to the water and prop slip?

ie. two Nordic Heat's with the same x-dimension. One weighs 10,000 lbs. the other weighs 100 lbs. The heavy boat would have the prop deeper in the water than the light boat. The heavy boat probably would not have problem grabbing water. The light boat would now have a prop that was more in the air, making slip very high. The light boat would have less drag for sure because less boat was in the water, but the slip would be really high because the prop was so high.

I am thinking that changing the prop depth with shorties or spacers needs to be adjusted in some relation to how deep the prop is in relationship to the water, which has some to do with the weight of the boat, and some to do with how high the boat sits on top of the water while planing.

I know that when I went to an all carbon hull on my pro jetski, the boat would sit almost 1.5 inches higher in the water than my other boat with a production hull. I had to manufacture a much deeper scoop on the intake to the jet pump in order to get the carbon boat to hook up.

I think that there are several reasons why some of Heats like prop spacers, and some don't. One is propably x-dimension, the other is probably boat weight.

So do you think these lighter (wood-free) Nordics are going to need some prop depth adjustment because they sit higher in the water?

I would love to hear some thoughts on this.

Chris

To continue the saga:

Boat was un-runable with stock prop depth of 3.5 inches from bottom of keel to prop shaft centerline.
Boat ran much better with 1" spacer making prop depth 4.5 inches from bottom of keel to prop shaft centerline.

Third outing in my new Heat.

Ran my boat with 3/4 of a tank in each side (more fuel than I have ever run), and six people in the boat. Two guys in the buckets, and four skinny ladies on the rear bench. ie... more weight in the rear. Fairly smooth water. Slip went from .143 to .124

Progress:

Initial boat speed = 78.4 mph 19.2% prop slip
1 inch spacer speed= 80.1 mph 14.3% prop slip
3/4 tanks and six people = 82 mph 12.4% slip

Any thoughts?

Try a P5x ?
Try a 1.5" spacer?

Chris

Here it is :eureka:.............
Steve

Odd..................

Are you still sitting too high? It just seems odd to me that could be the case but give all the extra weight and the added speed would certainly seem to be the case.

What is the motor weight compared to mine?

My slip is down around 8-9% and I can't swing the big wheels.
I'm on the verge of getting ready to order a 1" shortie and a 1/2" spacer at this point and I'm at 4.5" to CL of the prop shaft.

Could I be sitting that low, no way..

Southocg,

I think it also has to do with the balance of the boat. My boat is a bow-rider, and therefore has more weight on the nose than yours. The fact that I can put weight in the rear seat, and go faster, indicates to me that a deeper prop depth might be in order. I need more bow lift for sure. According to Mercury Racings website your Illmore motor weighs about 200 + pounds less than my 600sci. But you also have a wood transom, and I have a composite transom, which is lighter. Your boat has got to be lighter overall, but probably has a greater percentage of that weight at the rear of the boat, pushing your prop deeper in the water. You also have more horsepower, and therefore are able to lift the nose of the boat easier, which also puts the ass end down more while running. Steve Z explained to me that it is like a teeter-totter, with the pivot point being the step in the hull.

I am also going to try a P5x at Steve Z's recommendation. What was your experience with the P5x ?

Chris

P.S. I definately feel that you need to go up 1/2 inch

I'll give you a call later today.

Jim

Update:

My best speed to date has been 81.6 with a 30 B spinning at 5100 with weight in the ass end. (four skinny ladies)

Tried a 27 P5x today and went 79.7 right at 5400 rpm. Really liked the way the P5x carried the boat. My speed at 3k and 4k rpm was up about 3-4 mph. I am going to try a 28 p5x which should bring my rpm down to about 5200, and gain some more speed.

Chris

P. S. still thinking about dropping the drive another .5 over the 1" spacer I have installed because the boat picked up 1.5 - 2 mph with weight in the ass end when spinning the 30 B. Best speed with a light load and the 30 B was 80 mph.

I'll try to call you tonight. I have been at Powell and Havi for the last 2 weeks. But got your message.

Good talking to ya,

Chris

Interesting thread.

My prop depth was too deep. I recently changed to an IMCO shorty.
My boat seems to now run as fast with 3 people + fuel in the boat as it does when I'm solo on fumes.
This wasn't the case before.

I've heard of people adding weight in the back of the boat on either side of the motor.
I can see how it would change the balance, help keep the rear down, and let the bow fly a bit more.
Haven't tried it myself yet, but is an interesting concept.

I'm in a 26 outlaw with a 600sci.
With no steps, I really need the bow up to run.

ok I have to add to this also. i bought a 32 merc, labed bravo which zuck had reworked for a heat and i have now had it repitched to a 32 and added even more cup to it. I have the same prop depth as steve with a standard length imco with a one inch spacer now remember a 2001 is higher than the rest. ok back to my setup a supercharged 540 with lots of goodies running 7 to 8 pounds of boost at 5950 rpm loaded with fuel or not, peg and I ran 97 on the gps at the regatta when we ran to the dam. my boat does not like the five blades at higher speeds , well its so bad you cant drive it. I tried a 34 bravo and it also chine walks real bad I think its to steep of a pitch for a single setup the five blades work great up to about 91. this winter I am planning on trying a standoff box hoping to hit that dollar mark.

Jerry,

Thanks for the info !

Ever think about running trim tabs mounted parrelel to the water instead of parralel to the hull. I was able to calm my 91mph Eliminator Eagle down without loosing speed. Before changing the angle of the tabs, I was not able to get the boat much over 86 without it chine walking so badly.... I thought I was going to die!

With the tabs mounted flat, the ride was extremely stable.

How is the boat with the spacer removed?

Chris

Eliminator Eagle steering
 

Chris,

what kind of steering is that on your eagle? it looks like you have the short throw rams on there and that's what i need for my heat. if you don't mind, maybe shoot me a call when you have a chance. i have your number from a previous conversation we had but didn't know what would be a good time to call.

thanks
Ned
206.919.4194

my prop slip is about 22% without the spacer and the trim is worthless. i belive the four blade is the way to go it doesnt have the cruise speed of the five blade but its much faster. the 32 thats on it now works great its like driving a car down the road. if the standoff box doesn't yield anymore mph, I will change gears and go with a smaller prop and see what that does. right now zuck and i have tried every prop in nashville and were both back where we started. I'll give the tabs some thought.

Jerry,

Have you talked to the head guy at IMCO Nevada? He has a Heat with a standoff box. His name escapes me right now.

Chris

no i tried to find someone who has installed one even nordic and nobody had any info for me.

I've got an 05 w/525 and xr/its. Orig setup was with a slightly tweeked Bravo 1 and 1.5 gears. Best speed was about 78-79. Never tried a 5 blade with those gears so I can't give any input. I changed gears to 1.35 or 1.36 (I forget)... had to down pitch to a 26B1 and labbed it to 25.5. Best speed was 82 but the speed it inconsistant. Somedays it runs great and some days not so great. I recently purchased a P5X 24 pitch and at first I thought it was great right out of the box, 79 mph up top and good acceleration. Cruise speed was good and the boat carried well. I've now come to the conclusion that I don't like this prop. Here's why... The Boat handles like crap at high speed. It seems to be "Flighty" constantly trimming up/down to get the sweet spot and really can't find it. I'm constantly playing with the tabs to keep the nose down when the water gets rough. Maybe because of the ITS setback of 7" I've got more leverage. So... off came the P5X and the labbed B1 is back on. I forget to mention that I've got a 1" drive spacer, which works better for the 4 Blade. I haven't tried taking out the spacer with the P5X. I haven't had the time. Steve Z feels the 5 blade doesn't seem to matter much with the spacer in or out, but does help with the 4 blade. Just my 2 cents.

Best of luck

Ray

An IMCO "employee" did put a Heat together 2 or 3 years ago with a "800" HP motor, Imco setback box and modified bottom.
The factory removed the inboard lift strakes behind the step, looking for more lift.
I asked Lonnie Fluent at the 1st East Coast Nordic Regatta about the boat. In classic LF style he said "it's running pretty good, in the 90s, but we don't have the final #s"........
"it sits really bow high at at idle"........
And that's all I ever heard about it. Bob Lloyd did see the boat at the factory. Maybe he has more information on this boat?
Steve

I've got pictures somewhere. I'll try to look tomorrow. I got the feeling the boat never did work really well, but never got any first hand answers. It had a transmission in the standoff box for the IMCO SCX drive. So, it had a lot of weight hanging of the back. My Heat had the ITS. IT ran mid 90's with 900hp. That was running a 29 P5X at 6200 rpm. It always handled beautifully. However Nordicflames buddy in Utah tried the P5X on his Heat with about 1000 hp and didn't like the way it handled at all. It did not have an extension box. I never felt I gained any speed with the ITS, but it did handle speed better than any Heat I've ever driven.

chrus do you have the stock imco add on steering ram. if so do you want to sell it. thanks jerry

Jerry,

Sorry,

Already gone.

Chris

5 blade props
 

Guys,
Just an FYI on the 5 blades I've run.
All the Hydromotive P5-Xs, regardless of pitch or modification level have been fast and stable.
All the Maximus I've run have been very efficient in the midrange, but due to their large diameter are hard to turn on top end and take some driving, because they are trying to twist the boat around.
The new Precision that I tried (a 30") showed very good midrange speed, and was also stable. Since my motor is tired, I really couldn't turn it (88 @ 5300), but It did show a lot of promise. A fresh motor and some minor tweaks would make this one work.
My conclusion is to take the P5-X out of the box and go to the lake.
Regards,
Steve

I 2nd that what Steve said about the P-5 X. I have a Whippled 496ho and turning a 26p at 5300 to 5400, and love the prop right out of the box!!!

Re-post of response in prop slip thread:

I spent all day Friday and Saturday doing back to back prop testing. Things were facilitated by Tim of OCM. We tested props at 4.5" depth (1 inch spacer) and then re-tested with prop depth of 5" (1.5" spacer). I have always felt that my boat (an open bow) didn't carry the nose high enough. Testing has now confirmed this, as going to a 1.5" spacer brought my speed up between 1.5 and 2 mph across the board. I was afraid that lowering the outdrive would drop my rpm's because of more prop bite and outdrive drag. Instead, the outdrive lifted the boat up more, thus reducing boat drag more than the lowered outdrive increased drag. The result is that I gained aproximately 100rpm on top end while reducing slip. At this point, the bravo 28 and the 30 bravo are both running 81.5 mph +/-. The 28 is just kissing the rev limiter at 5400, and the 30 is a little lazy getting to full speed. The 27 P5x is also just barely hitting the rev limiter, but is about 1 mph down across the board. Prop slip on the 28 Bravo is the most efficient of the bunch at 11.6%. My boat now has a more "nose up attitude" running across the water, and just plain feels better! At this prop depth (5" from keel to propshaft centerline), the 4 blade props are beating out the 5 blade props in both cruise speed and top end. The increased outdrive depth, decreased slip on the 4 blade props, but did not really affect slip on the 5 blades. The exception to this was when I tried Tim's 29 pitch, 5 blade, round earred, Herring. This prop was a little too big for my horsepower, but exhibited 9.8% slip. My cruise speed at 3000 and 4000 rpm went up 7 mph effortlessly. Top speed was 79.5 mph at 4800 rpm. This prop was extremely smooth in every way but the pricetag. My summation of this test is that open bow boats probably need more outdrive depth than the closed bow boats, in order to better carry the bow.

Special thanks to Nordic and Tim of OCM for making this testing possible by supplying props, outdrive spacers, and time.

NORDIC ROCKS!!

I will continue testing,
Thanks,
Chris

P.S. Steve, My son inadvertantly left the 28P5x Labbed prop at home and I was really bummed. I will be testing this prop, the next chance I get.

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