Baffled by prop test results

[Mr. Demeanor]

Spent some time with Ken from PropGods today and can't say enough good things about him. We did some prop testing with my 23’ Concept center console powered by a 200hp carbed Merc Saltwater. Gear ratio is 1.87:1
Engine height is conservative with cav plate just out of water. I lose speed if I go higher.
My current prop is the 21 Trophy listed in the results.

Mirage Plus 21 5800rpm 54mph / 38mph
Tempest 21 5800 rpm 54.2mph / 37 mph
Enertia 22 5800rpm 53mph / 40mph
Trophy Plus 21 5900rpm 54.5mph / 34mph cruise (Rev Limiter)
Trophy Plus 23 5800rpm 52mph / Didn’t check cruise
Trophy Plus 25 5500rpm 52mph / Didn’t check cruise
Bravo 22 5700 + rpm 53 / 38 Took forever to get up to speed. Needs PVS

I think the cruise is bad on the Trophy’s because of the exhaust running over the top of the small hub. I have ordered an exhaust seal ring for running the small hub prop on a large gearcase. Should be in tomorrow.

The Enertia looks great on paper. It accelerated very hard and had the best cruise, What I didnt’t like was how easily it blew out. It was fine and then one little tap of the trim button and it blew out hard. It would be very hard to trim for speed and keep it there.

Cant figure out why the 23 Trophy Plus ran poorly. I thought that would be the prop for me. I just needed to bring my rpm down a little but only lost 100 rpm but lost 2 mph????? I examined the prop and it looked fine.

The Mirage Plus and the Trophy Plus were a dead race for top end. I will have to check cruise after I install the exhaust seal ring on the Trophy.

The Bravo was the only prop I could trim all the way out and it stayed hooked. If only it didnt’t take 3 miles to get up to speed.

I got my best speeds when the prop just started to ventilate. RPM would go up and speed would follow about 1mph. I think that why I ended up running almost the exact same rpm with every prop. A little more trim and speed would start to drop.

The Trophy results just don’t make sense. The 21 has a slip of 13%. The 23 has a slip of 23% !!!!! If slip would have stayed the same, I would have been running 58.8mph which is what I was hoping for. The boat is running 6mph faster then when I bought it and all I added was a manual jackplate so I cant complain.

Any thoughts on these results is appreciated.

[dlivewyer]

Cant figure out why the 23 Trophy Plus ran poorly. I thought that would be the prop for me. I just needed to bring my rpm down a little but only lost 100 rpm but lost 2 mph????? I examined the prop and it looked fine.

I'd say that you have a GOOD 21p, and a piss poor 23p. You can't tell by lookin' at 'em. :confused:

They don't all run the same. You could run 5 trophys of the same pitch and probably get different #'s with each one of 'em. Try a different one. ;) The 23 is your prop tho'. It just needs fixin'. :D

Send it to mark croxton for a b/b and a little xtra cup on the tips. He knows how to get it runnin' right. :cool: I bet you'll get that 4 mph. ;) He has done a few for me and they were a different prop when I got 'em back. :cool:

[The Big Al]

The Trophy results just don’t make sense. The 21 has a slip of 13%. The 23 has a slip of 23% !!!!! If slip would have stayed the same, I would have been running 58.8mph which is what I was hoping for. The boat is running 6mph faster then when I bought it and all I added was a manual jackplate so I cant complain.

Any thoughts on these results is appreciated.

Trophy's
They are a breed all their own. The biggest problem with them is from pitch to pitch the never never add up! And you can take 12 of the same with same pitch and every dam one of them will be different.
I have no need for a Trophy.
But they do have their place, and when they work they work very well.

Also before I go prop crazy, adjusting the Jack plate can help you out greatly.
Trimming up and getting slip tells me you need to adjust it.
Get that engine back in cleaner water.

Now, looking at your info. Seems your against the rev limiter hard.
Should have keep going up on pitch till rpm came down then go back up.
5800 rpm is the factory limit on that engine. You could be against it with a 22 or 23 or 25 Keep going up till you see a 5500 rpm then go down one pitch to get back to a true 5800rpm You could be just waisting power & torque.

The trophy just might be your prop, but not being to high out off clean water and high the four blades remove the water and slip.

Adjust that jack plate with every prop!
Every one, even if same type, their is no magical setting. Every prop has it's own sweet spot. High setting is not always the answer.

If your looking for top end, i would bet it's going to be the Tempest. Get a 23p and try it.

Also calculate the fuel weight you were burning during all this testing.

[Fast Fred]

if it was mine, i'd try some cup in the 21trophy plus to keep it just under the limiter, maybe add 1/2" of pitch. the 25 is lookin to long.:cool:

[staylor]

...Trophy's don't have much cup at the tips. A rework adding a bit more tip cup will allow the prop to run with more height/trim without starting to ventilate. This alone normally drops the revs by 100 or so. When the prop is blueprinted, the shop will equalize the pitch on all 4 blades and if you tell them, they can hold pitch on the high side or low side. As for the 23 Trophy, you could probably get this to hook up, but I suspect your revs will be too low. If you do the math in the merc prop book you will find that on your rig, the 21 Trophy has a better angle of attack and hence runs with a bit more efficiency than the 23. This is common when you're just running too much pitch. As for the added ring, this is normally used only if the prop won't hook up out of the hole with all the vents plugged solid. It can cost you a mph or 2 at higher speeds since it's blocking some of the exhaust and thus building some back pressure. Both Mark's and Boger Props do very good work on Trophy's.
Doug

[Mr. Demeanor]

Ill give them a call and see what they think.
My prop-shaft is currently 4.5" below the hull !
That is 2.5" higher than stock with the motor in the top holes
I took this pics to give you an idea of the setup. The red line is what I think is going on. I think the water coming of the pad is coming up at a fairly sharp angle back where my motor sits. It is hitting the cav plate and being deflected back down around the prop and thats where the slip is coming form because the water is dirty. Two reasons I think this may be whats going on:
1. I keep raising the motor and the cav plate is above the water but there is a lot of spray coming off the bottom of it like its deflecting water coming up.
2. Before the jackplate, I had a problem at cruise where the prop would occasionally ventilate for no apparent reason. Thats when I saw my cav plate was under water. What happened was the cav plate would surface, grab a little air, and force the air down around the prop which would slip. When it slipped, the cav plate would go back under and the prop would hook up. I actually watched this happen over and over hanging off the back of the boat which would porpoise lightly as it happened. RPM would go up and down about 200rpm. That stopped now with the jackplate but maybe the plate is still in a bad spot.

If I raise the motor more than another 1/2", I start to lose speed. That is still 3.5" below the pad. Maybe I just need to crank it way up (even with pad) and see what it does???

I would like to find some more answers before having prop work done but I am moving in the right direction. Speed is up 6mph over stock and the annoying cruise slip has stopped.

http://img.photobucket.com/albums/v399/MrDemeanor/Boating/17PDN184.jpg

[Hottrucks]

one issue no one has addressed is the change in Rake between the 21 and 23.......If you can find yourself a 23 offshore merc and give that a spin

thats my .02

[Mr. Demeanor]

I have a 21 Offshore in the garage. It ran the best until I raised the motor.

[staylor]

For a boat of this type running at the speed you are, I think you are about as high as you can get without venting. I'm running a fishing hull, vee type in the low 60's with propshaft at 4 inches below and only a slight positive trim. Any higher and I start to vent with Tempest or a modified Trophy.
Doug

[Mr. Demeanor]

The only other option I think I could try would be to crank the hieght way up and see what happens. Maybe go an inch under the pad and just try it. As long as I hold water pressure it cant hurt to try. Maybe Im just in bad area and need to try a big change to get a baseline.

[Mr. Demeanor]

See all the black carbon on the front of the hub. Thats form the exhaust blowing out. I installed the exhaust seal ring today so I will run it as is first just to see if the slip numbers change.

[The Big Al]

If that engine is on the border line of being to high, Then you have a very very heavy front end on that boat.

Now, props with more lift (most results from cupping) The lower the engine runs in the water.

The back of the transom is the pivot point!

If you raise the bow, you lower the engine.

Also all measurements are from to the bottom of the boat, BOTTOM
Not the back and the end.

From the bottom flat part of the boat!

And it's only a reference point.

Like I said, their is no magical setting! EVERY PROP is different.

If you have a heavy tank, then Trophy could be your choice.

But your going to need it worked!

This would have a big effect on the prop letting loose.

Pic the one you feel has the best out of the box performance and send it off.

This is why you have high slip numbers, working a prop and cupping it will help.

I would send it to a knowledgeable shop, Performance Propeller, Soddy Daisy Tenn.
Talk with Tim or Billy tell them your problems and needs. Let them decide what the prop needs. Let them do their magic.
http://www.performanceprops.com/
Al

[The Big Al]

Your Green line needs to run under the boat and flat against the bottom.

The prop shaft should be parallel to that line.

Notice the blue line your showing for the prop shaft is running into the trailer and NOT Parallel with the bottom of the boat.

The green line should be parallel with the cavatation plate also.

Engine is trimmed up in this picture

http://img.photobucket.com/albums/v399/MrDemeanor/Boating/17PDN184.jpg

[Mr. Demeanor]

The green line is running flat off the very bottom of the hull and hits the 4th hole up on the intake grate just as I drew it. Because the pic is at an angle, it looks like its angled up a bit. I held a 10' 2x4 against the bottom of the boat to get the measument. The rest of the measurments were taken from there. The propshaft (blue line) is 4.5" below. The cav plate is level with the bottom of the boat (neutral trim). I jsut have the bow of the boat down low so I can get under the stern to take measurments. Its just the angle of the pic that throws off the way the green line looks.
The props pretty deep and this boat has no weight up front. Boat weighs 3000 pounds dry with motor which is light by center console standards.
The problem with going real high on a boat like this is the prop blowing out when plowing throw waves like when we troll. I think I may try raising the motor up significantly just to see what it does. Doesnt cost anything to try. If it did work at a much higher height I could go to a 20" shaft and lose the jackplate.

[Mr. Demeanor]

Do I measure setback from the notch (where the drain plug is) or from the actual transom (where the trim tabs are mounted)? And where is it measured to...leading edge of prop, nose of lower unit, etc. ????

[The Big Al]

OK, i see that.

For the amount of setback, that engine is low.
But who knows? Every boat is different. No matter how much they are the same, they are different.

I would pic the Trophy you feel is best, send it and get it worked.

The exhaust ring will only effect hole shot. ( butt again you never know)

Send it to Performance Propeller, Do not tell them what to do.
Tell them your problem and what your trying to accomplish.
Let the Prop guys do what they do best!

I promiss you! This will work!

Al

[SportJ-US-1]

Ill give them a call and see what they think.
My prop-shaft is currently 4.5" below the hull !
That is 2.5" higher than stock with the motor in the top holes
I took this pics to give you an idea of the setup. The red line is what I think is going on. I think the water coming of the pad is coming up at a fairly sharp angle back where my motor sits. It is hitting the cav plate and being deflected back down around the prop and thats where the slip is coming form because the water is dirty. Two reasons I think this may be whats going on:
1. I keep raising the motor and the cav plate is above the water but there is a lot of spray coming off the bottom of it like its deflecting water coming up.
2. Before the jackplate, I had a problem at cruise where the prop would occasionally ventilate for no apparent reason. Thats when I saw my cav plate was under water. What happened was the cav plate would surface, grab a little air, and force the air down around the prop which would slip. When it slipped, the cav plate would go back under and the prop would hook up. I actually watched this happen over and over hanging off the back of the boat which would porpoise lightly as it happened. RPM would go up and down about 200rpm. That stopped now with the jackplate but maybe the plate is still in a bad spot.

If I raise the motor more than another 1/2", I start to lose speed. That is still 3.5" below the pad. Maybe I just need to crank it way up (even with pad) and see what it does???

I would like to find some more answers before having prop work done but I am moving in the right direction. Speed is up 6mph over stock and the annoying cruise slip has stopped.

http://img.photobucket.com/albums/v399/MrDemeanor/Boating/17PDN184.jpg

You need to make all your measurements with the prop shaft parallel to the bottom of the boat. Not at an angle like you are doing. It changes the measurements. I think you are still to low (thats the reason for all the spray you mentioned) with as much setback is built into that thing.

[Mr. Demeanor]

It actually is parallel in that pic it just that the bow is cranked down real low and the angle makes it look like the boat is sitting flat. My driveway is ripped out right now waiting for pavers and that concrete is the new pad I just poured (16'x44') along side the house for boat parking. I cant get the boat up on the pad as it stick up too high.
I actually took the measurments awhile ago after leveling the boat and then leveling the drive using the cav plate. I just didint take pics to illustrate the setup then.

I am using a 0-100psi water pressure gauge that I just hold while testing as I dont have room for a permanent gauge. The range of this gauge is too large as I cant tell when I start to lose pressure. My motor makes about 18psi. I bought this one at Home Depot but cant find anything say 0-30psi. Any idea where I can find a low pressure gauge?

[Hottrucks]

some thing else you might try on your best prop is to glass beed the egde of the blade sbout 1/2" down including the cup this will make the water stick a little longer ( acelerate the water leaving the blade) also lower how soon the prop blows out
ok now I'm up to $.04

[Mr. Demeanor]

Yesterday I tried an exhaust seal ring on my Trophy and it did bring cruise speed up a couple mph. I didnt get a chance to do a top end run as I had a full load of guests and gear on the boat.

[Mr. Demeanor]

After playing around with the height some more I found that any higher and I lose performance. From 4" - 4.5" below the pad to seems to be the sweet spot.
I like the Top end of the Trophy Plus but the cruise is down a few mph. Better since I put the seal ring on but still low. I will probably end up with a labbed 21 Mirage+ in the end. The Enertia was slightly better but blew out without warning then wouldnt hook back up without trimming way in and starting over. The Tempest felt a little loose even at my relatively slow speeds.
The Mirage+ is such a common prop that I can probably find one cheap and have it worked over.
If I ever find a real cheap 22 Bravo I may have some PVS type holes put in it and see how it runs. Then I could probably raise the motor a little higher.
Thanks for your input.

PS. Todays catch was four nice Kingfish (limit) that made for a nice dinner and we lost two big fish. :)