finding the right prop
 

looking for feedback on finding a prop...

My boat: 23 CC rebuilt a little lighter than stock. Yamaha F225 on a bracket.

First prop was too small; 13.75" diameter and 17 pitch aluminum, it ran too high RPM.

Second prop caviation issues; 15.25" x 19 pitch, but it was a vented prop (holes in hub at base of each blade).

The second prop performance was a little strange to me. While the first prop held a nice grip until the motor was trimmed up more than half, the second prop would cavitate at anything other than all the way down/tucked in. At slow speed it was tolerable (although I could feel it a little), when running anything over 4100 the venting really was noticeable. I was still able to get 6000 RPM and 40 mph - lightly loaded. 22 mph at 4000 into (we had at least 15 knt wind), and 25 mph at 3800-3900 down wind.

Another wrinkle: second prop hub diameter is 1/2" or so less than gear case. It stood out to me as not looking right. below is a picture. Im sure this could explain a lot of the cavitation/venting also, there must be a huge amount of suction generated by such a drop in diameter.

http://i19.photobucket.com/albums/b2...ine/prop_2.jpg
http://i19.photobucket.com/albums/b2...ine/prop_1.jpg


I sent the second prop back by UPS today and will see what the shop sends back for prop #3. Seems like a 18 to 18.5 with a 15.25 diameter will be just right

Any ideas on that hub diameter?

Hub diameter is wrong. Exaust is either escapeing between the hub and lower unit or being excessivly sucked through the vent holes due to the decrease in hub diameter. Thats your cavitation problem.

I would try a 15 x 17 with the right hub diameter. That prop in the picture dosen't appear to have much cup ( Trailing edge of blade has a slight fold or "cup" to increase bite). Seacrafts like some cup in their prop. It provides stern lift. Stay away from a prop with cup on the tips. That can produce too much bow lift.

Post up on propgods.com and Ken could help out.
They also do this as a service and I will be trying them out soon.

i am running a 15 x 17 on 23 cc 225 yami , armstrong bracket, light load i turn 6000 and run @44 on yami gauges, i do seem to have little to much bow lift and and a little disappointed on hole shot , especially with a full load of fuel? might get the cupping checked . Maybe try a 4 blade for hole shot but don't wanna give up to much top end. Oh and also need to be able to stay on plane at a lower speed. I am also coming of a 23 with a 2 stroke 200 on the transom. Not trying to hijack the thread just giving you some feedback on what i am experiencing with a very similar set up and also looking for feedback myself. Are you using propgods?

thanks for the link to propgods, once I get a proper fitting and non-vented prop I will get some good data and take it to them and buy a "perfect" prop and turn the other into my backup.

The second prop test was not worth much, with the vented and too small hub.

thank you for that. I think we will be pretty close, the first prop I used was a 17 pitch but the diameter was smaller so my RPMs were even higher.

I don't think there's one that covers all situations, kinda like the multi boat theory. I'm running a Solas 4 blade 17 on 23' w/Hermco bracket, 250 Yam 2s. Cruise high 20's-30, tops ~ 40 but holeshot is good and lower planing speed when rough. Typically ~ 2mpg. The 3 blade 19 runs faster and will hit low 5k rpms, holeshot is acceptable, but have to run a little too quick when rough.

Hey Shine, theres nothing wrong with a little ventilation at the initial burst of throttle to get on plane. It helps the engine build rpm. Its easier on your motor to jump on plane rather then just easing it up.

I think Reelescape makes a good point regarding different props for different situations but finding a good all-around prop that covers 80% of your applications shouldn't be that tough. Most SeaCraft ccs need some stern lift from a prop.

I think this and all prop discussions would be a lot more meaningful if the props are identified including make, model or model number as well as material, diameter and pitch and number of blades.

Different prop shapes are designed to do different things.
Diameter and pitch are a part of the equation but with the wrong shape, cup, or rake, you're pulling wheelies instead of getting on plane efficiently.

Obviously in this group there will be differences as people have shifted cg around by moving tanks or batteries, or adding pilot houses or brackets, etc. Others lightened their boats dramatically by shedding pounds of wet wood replacing it with composites.

Shine, I think your f225 has a 4.75" gearcase, but double check that... PowerTech Props has some quality stuff at real fair prices. Maybe you prop guy carries their line. Check out the MQS and SCE models. they come in 3 and 4 blade and mimic Mercs Black Max and Yammies own Semi-Cleaver. Great stern lift and all around performance. Very informative site, too. www.ptpropeller.com

Godsreel, I think a 4 blade typical helps any SeaCraft with a big 4 stroke especially if the pointy end is riding too high. I don't recall if you're running a 4 stroke or not, but either way, I'd give up a barely noticeable mph or 2 @ wot for better hole shot, handling, and cruise efficiency every time.

Good luck guys and try to post your results and prop info when you get dialled in.

I will say as far as props the Stilletto I bought is awesome, very aggresive so be careful not to over pitch as it will be 300 RPM lower than the same as others, but it will hang with great trim response. Moving my motor up 2 holes this week, they are bad azz, which will put me at least 2" above hull bottom. I will report back after the change, its about 1" now but I never cavatate even trimming way up so up she goes.

I am going through the same thing. I have a yamaha saltwater series 17 by 15.25 three blade. The engine is an F250. Also on a bracket. It seems as though my cruise is at 4500 at 26 kts burning 10.5 gph. I haven't really pushed it in good conditions yet to see the top end, I will let you guys know though.

What was weird is I went out straight into 2-3 footers, and a 15kt wind the nose stayed down the ride was dry and smooth, no porposing at all. I was thinking man I can't wait to go down sea and let it scream. I turned down sea and the but was up and down, and I lost 3 kts at the same RPM. Ride became a little wet also. Also as soon as I drop below 4300 RPMs the boat is flirting with coming off plane. I am a little bothered by how high I have to keep the RPMs to stay on plane. I am seriously considering the 4 blade prob...

That is pretty much exactly what i am experiencing, how much top end do you guys think i would lose going to a four blade prop?

Godsreel, Honestly I don't think you'll lose squat on top end (well, maybe stern squat). With a 550-600 lb 4 stroke motor hanging 2+ feet back, a 4 blade will only benefit you. The Potter hull was designed for a 400 lb motor to ride on the transom. And while they did put twin 200s on they didn't plane a low speeds either. Heavy 4 strokes were probably a contributing reason for the evolution of the 4 blade prop

Jr. those RPM's seem pretty high, fuel burn is a lot for a 4s. My budy has a new 23 SC (euro transom so they call it 25) and he gets the same fuel burn with twin 150 optimax, and few mph faster

Are you running with a heavy load, do you have trim tabs?

My hull is a 1972. It was rebuilt and is pretty heavy. I had about 100 gallons of fuel on board. I think that newer hull is probably a lot lighter than this. Those optis are supposed to be pretty good on fuel. Also I have a t top and an eisenglass front window which I think catches a lot of drag.


Another thing is that I am pretty sure I am getting some cavitation from my transducer. It's a transom mount mounted too low and in the middle since their used to be twins. Time will tell.

Also if you look at the performance between comparable boats on the yamaha website the 23 regulator and 23 sailfish seem to have similar specs to what I have seen. Only thing I can see is that I may want to try a prop with more pitch I guess, which doesn't make a ton of sense, but it seemed like the 23 sailfish with the 19" prop performed better.

You guys close enough to Chas SC are welcome to ride with me or run
mine to check out the 4 blade on 2S 250 :)

4 blade 19 pitch on its way from propgods :) Will run it up and down the Indian river this weekend and report back :D

Sounds good. Was it a rental? I need to get a 17 4 blade re-hubbed then I can try it. For now I need to haul out and move that stupid transducer.

copied from my post over at propgods.com......


27.7mph @ 3800
42mph @ 5600
30mph @ 4100
25.5mph @ 3600

20 mph beam wind, same rpm/speed running both ways up and down the river.

Load was 55 gallons fuel, 2 guys, full live well (about 360 pounds), with empty baitwell the speeds/rpm were the same but the hole shot was even worse. A little trim tab solved this.

5600 was as much as I could get without trimming the motor up too much. Prop really grabbed well, no problem keeping on plane at low speed, felt great. 3800 to 4000 seemed to be a really nice cruise. Hole shot was terrible but I expected as much.


AND

F225 manual says under a full load, the RPMs need to be in the upper half of the full throttle range. Full throttle range is 5000 to 6000. I was not at a full load and barely getting into the upper half of full range (5600).

I just wish they made an 18 pitch !

Solas has a 14 1/8 x 18

4 14 1/8 18 R 3553-141-18

thanks for that !

Huh... I am temped to throw the 19 pitch 15.5 saltwater series I have on there just for kicks... I guess my slippage was pretty high, I am not sure what the answer is, and it doesn't sound like anyone is. The good news is that I fixed the cavitation issue, the bad news it didn't help performance though.

Hole shot should be great with the right prop. Just my opinion but I say its way too much prop. You need to gain 400 rpm minimum from where your at now. A 17 pitch in that lower diameter 4 blade or a 15 x 17 3 blade will get you there.

What was the diameter on that 19 pitch 4 blade you had? Is the 17 the same diameter? I think just the pitch change alone should get you the extra RPMs. At the same time I think that may be the prop I need.

I am thinking about gettting a new 300 to help with the hole shot. I'm working on putting together a team for the armored truck heist. LOL

IIRC Yamaha makes an 18 pitch 4 blade, a guy was selling one up here on the NH or Boston CL for $275. 1 think 13-3/4 x 18, but there might be other sizes (for $500+ new!)

Yamaha lists it on their website-

13 3⁄4 18 4 Performance 4-Blade pressed in MAR-GYT4B-V6-18*

2" pitch in the same dia. will yield almost exactly 400 RPM - a 23 should have a decent Dia prop as well - I am not familiar with 4 blades other than pitched correctly top end loss has been only about 1mph that I have seen. Mirage+ had been pretty popular here, large Dia, good cup and progressive pitch - means pretty aggressive. The Stilletto and Tempest are also progressive but I would not recommend a Tempest for this application BTW my shop Piper Marine in Tampa had a used 17 Mirage+ for around 225 at one time.

That being said none of you are raising the motors - I mentioned earlier I was - ran it this weekend. First I removed an old thru hull transducer - then measured the engine - it was pretty high at least 1 -1 1/2" above the hull already so we only did 1 hole which is about 3/4, so 2"+ now.
Picked up 1.5 mph at cruise from 28@3400 to 29.5/30@3400/3500 - top end picked up 100/150 RPM to 5600 and 3 mph to 52. Prop still would never break loose regardless of how high I trimmed it or turned it. Odd thing, motor changed pitch at 3000/3200 ? used to have a marked change in pitch before, sounded almost like laboring - gone now? Motor sounds much happier

Props on 23's should be vented, pretty big boat to run correct top end and they should be vented for hole shot help IMHO

Stilletto 19" Merc 200XRI - when changing props, this prop did pick up the whole boat and made at it least twice as dry with amazing trim responce - I only bump it if needed. You could not get it from me without a gun - just say'in

Check the engine height before doing much more with props, if thats not right it will never run as good as it could - brackets are different because of the set back - you guys are on your own there I don't have one

my motor is 2.5" higher than bottom of transom, no issue there.

Have decided to go with a larger diameter 3 blade 15.25" by 17 pitch. the 4 blade I tested was 14.5, so I am hoping to get a little less slip.

To this point I have just been trying to find a prop that will match the boat/motor well enough to operate. Assuming I have done that now the big 3 blade 17 pitch, I want to now dial in the fuel efficiency......Ordered a fuel flow meter, it does not make much sense to spend a lot of $ on props and and gas when you dont even know the efficiency of the changes your making :)

for what its worth I re-ran my slip numbers after raising the motor - before was 14% at cruise a 11% above 4K

Now its 11% at cruise and single digits 7% at WOT - I am using 1.87 gear ratio which I think is correct, been awhile since I did it.

will you fellows explain slip? Thanks

slip- is a calculation reagarding the efficency of the prop, you plug in your criteria - prop pitch - RPM- speed - LU gear ratio and the calculator throws a number up - 15% and under is good 20 or above you need to try something

Think of the prop as working like a wood screw, where a prop with a 17" pitch travels 17" for each revolution if there was NO slip. Add gear ratio, engine rpm and throw some constants into the equation to convert minutes to hrs and inches to miles and you can come up with a theoretical mph (with NO slip) for a given rpm. The % difference between the theoretical and actual mph at the same rpm is slip.

latest prop is big 15.25" by 17 pitch 3 blade from mercury. basically same as as Yamaha SW series II

42 mph at 5900, makes for 12% slip. Windy day, good sized fishing load (3 guys, gear, 80 lb ice, half full boat well, 50 gallons gas.

I'm pretty happy, did get a little venting in the sloppy conditions of Saturday. I could probably stand to lower the engine by one notch.

I think Im happy for now, might try to find an 18 one day

Before you lower motor, check where the AV (anti-ventilation) plate is when you're running up on plane, trimmed out where you normally run. Top of plate should be out of the water! Min planing speed is also a good thing to check when comparing props because bracketed boats tend to be a little stern heavy and often won't stay on plane below about 20 mph or more. A good stern lifting prop will help it stay on plane at a lower speed, like 12-13 mph, and makes the boat less throttle sensitive in a following sea.

Hey Shine those numbers look pretty good. If you have a prop shop nearby, have them add more cup to the trailing edges so the blades get a little better grip and that cavitation should disappear. Might even be able to raise the motor another notch as Denny stated.

might just do that! I want to get the fuel meter hooked up first so I have some better data. Of course, before that I have to get lights working, put in some LED's, install washdown, install spring locks on hatches, etc ....... :)

what is my slip with these numbers 17 pitch, yamaha four stroke 225 LU gear?,44mph, 6000 rpms? Three blade prop.

-2% in other words the prop slip computation calls bs on your numbers. :eek:

In theory the fastest your data would allow is 43 mph. I don't recall what Yammie youre running but you might double check your gear ratio. Seems they were 2:1 for a long time.

There are a host of prop slip calculators on line just plug in the numbers and brag:D

Here you go The actual calculations are above the calculator if you want to practice old school math:
http://go-fast.com/Prop_Slip_Calculator.htm

without doing the math myself, the merc prop calculator says you have 7% slip with those numbers..

http://www.mercuryracing.com/propell...calculator.php

oops, I guess misinterpreted the listed 225 to be 2.25 gear ratio as opposed to being hp. :o