Cured the porpoising issue... Well almost. (Prop question)

[Moose-Hunter]

Howdy all...

I dealt with a bit of porpoising with my new rig. Seems after following all factory specs and configurations, she was REALLY trim sensitive. Found out all the factory specs were correct for the big Yamaha 4 stroker, but didn't take the extra weight of the kicker into consideration!

After a bit of creative weight re-distribution, I have the bucking down to a very small window in the revs/trim... I'm ALMOST there!!!

Question... I'm thinking a prop designed for more stern lift would put me over that porpoising edge and back down to stable motoring. I'm currently running a 13 3/4" x 19 Yamaha Reliance SS prop. The pitch is about right since the WOT for this engine is 6K. I'm running 47mph at 5800 with this prop loaded "normally", trimmed up. But do blow out when turning sharp without dropping the engine. Not a problem really as it was trimmed high and I was just testing.

I think keeping the 19 pitch and getting a prop with more "cupped" blades would do the trick. Or even dropping the pitch an inch or so and going for a 4 blade.

What say ye?

[boatfixer]

What you want is a prop with more rake which will provide more bow lift. Personally Im not overly familiar with Yamahas prop selection, but I do know more rake is what you want.

[Moose-Hunter]

What you want is a prop with more rake which will provide more bow lift. Personally Im not overly familiar with Yamahas prop selection, but I do know more rake is what you want.

YES... Rake was the other component!

The Yam Reliance series has very little rake compared to other SS units of the same pitch and diameter from the aftermarket. More rake coupled with added cupping and possibly raising the engine one hole... I'm told this will work magic with this boat.

I'll most likely do the prop first. then test. After that, "maybe" I'll hook up the big ol' hoist and raise up the engine for more testing.

Your thoughts?

[boatfixer]

Looks like a Turbo 2+2 Is a 4 blade that is suppose to provide bow lift. Looks like you can getan 18p

[Sonicrunch]

I like cupped better that four blade.

Keep in mind if you go with a cupped prop, it will reduce your top rpm a just a little.

[Northlander]

I would not do any raising of the motor until you have tried other props. Call Jay Soderbloom and talk to him. He vented and cupped my stainless as well as thinned the blades a bit for my 115 yamaha 4 stroke and it did wonders. Quicker out of the hole, no more wash outs in corners and got a few mph top end.

[Down Deep]

Ditto on what Northlander said.....

[Moose-Hunter]

I would not do any raising of the motor until you have tried other props. Call Jay Soderbloom and talk to him. He vented and cupped my stainless as well as thinned the blades a bit for my 115 yamaha 4 stroke and it did wonders. Quicker out of the hole, no more wash outs in corners and got a few mph top end.

checked out the site and to my surprise... They carry my favorite brand of prop!!! My "stocker" will be put "in reserve" as my back up so mods are not really necessary. But... A new prop is in my future. And if testing the new prop turns out better than positive, maybe I'll try lifting the engine a hole.

One thing at a time. Weight distribution worked well, I hope the prop will fix the problem. And lifting "MAY" be a unexpected boost in performance. We'll see what happens next week.

Thanks for the help folks!!

[Northlander]

Unless your boat was totally set up wrong at the dealer you shouldnt have to mess with raising or lowering the motor. Try some new props and weight distribution.

[goose89]

Moose-Hunter, what hull are you running?? I'm guessing you've got a F150 Yamaha. I know of alot of pertinent info that may help you if it's the hull I'm guessing it is. Good luck...

[Moose-Hunter]

Moose-Hunter, what hull are you running?? I'm guessing you've got a F150 Yamaha. I know of alot of pertinent info that may help you if it's the hull I'm guessing it is. Good luck...

Hey Goose... The hull is a 17.5' 2XB Alumacraft. If it's a bunch of info, send it to my email addy... moosehunter42 AT embarqmail DOT com.

Thanks...

[Moose-Hunter]

Unless your boat was totally set up wrong at the dealer you shouldnt have to mess with raising or lowering the motor. Try some new props and weight distribution.

It's not so much that the dealer screwed it up. It's that I had a kicker installed and the added weight played havoc with factory specs.

I'll be getting a new prop. That's a fact! And using my stocker as a back up. I'm still playing with weight, but have limited "heavy" items I can move around. This has been the most help thus far...

The only way I'd ever try raising the engine is IF the prop I get is SO good and grips SO well, that raising the engine would have a positive effect on overall performance. I tried it with my last boat and it was a bust! This boat, with it's higher HP may react differently. Besides... It's a easy job with the hoist I have access to. Loosen two bolts, remove two bolts, tighten chain. Replace two bolts adding new marine silicon.... Done deal for the next days on the water tests. If it works... SCORE!!! If not... 45 minutes wasted. No biggie.

There's a real good chance I just won't try it. But then again... I like to tinker and everything is fair game.

[goose89]

Sorry Moose...not the hull I was guessing. Glass boats can be "finicky", but tin usually not.

I used to run a 2XB (175 TP CS) with a DF 140 Suzuki, T8 and a MK Vector on back. No porposing / cavitation issues at all.

Curious how you'd be having issues with a slightly short hull and more HP's.

How are you loading that boat?? 3-4 people? lots of gear? full fuel tank(s)?

Good luck.......

[Northlander]

A kicker should not cause you that much problems in that hull I wouldnt think. I have a Lund Explorer SS 17' and a 115 Yamaha 4 stroke on it and when I added my 9.9 yamaha 4 stroke kicker it made very little difference on the way my boat performed. No porposing/cavitating unless Im over trimmed. RPM's are still good and top end is the same.

I still think its a weight distrubution and propping issue.

[Northlander]

Moose what exact boat do ya have? 175 what? Competitor or Dominator Sport maybe?

[Moose-Hunter]

Moose what exact boat do ya have? 175 what? Competitor or Dominator Sport maybe?

Here she is fellas... Alumacraft 175 Trophy, Yamaha 150 with a T9.9 kicker.

So new, the numbers had yet to go on.

Weight in the rear... Man, that's a toughy. Main engine (Yam F150): around 480lbs which includes the tall transom extension on the shaft housing, Kicker is about 100. The gas tank (38 gallons) when filled weighs roughly 240lbs. Add in the weight of a 20 some gallon live well and a big battery... and this girl ends up with quite the hefty rear end.

And all this is the aft 1/3 of the boat.

To compensate... I have (2) deep cycle batteries up front (124lbs), a full 20 gallon live well (166lbs), down rigger balls (24lbs), 3 bank charger (22lbs) as well as misc gear in the dry storage. Pro seat, trolling motor, (2) graphs and lil' old me round out the front... Still I read her to be a bit heavy in the arse.

Like I said, I'm r-e-a-l-l-y close to having her dialed in with weight distribution alone. The prop change should do it. Then... I may (or may not) play around with engine height.

ETA: And if you're wondering... YES, she does fit in the garage. With the engine tilted all the way down I have a couple inches of air between the top of the cowl and the door frame. Same with the windshield. Never had a boat that could have been too "TALL" before. Too long...yes. but too tall??!! That's a new one to me. But she fits and life is good in the M-H garage!

[Northlander]

Ok I see your issues now. My boat has gas tank and big livewell up front. I do have small livewell, 2 batteries, main and kicker in back. My boat seems to like the weight more to the rear. Thats the thing about different boats. I now remember my neighbor had a Alumacraft that he carried almost all his extra gear up front. He wound up with a hydrofoil or whatever on his motor but he was underpowered with a 115 horse to start with.

[Moose-Hunter]

A new prop is installed and waiting for water testing. I went with a PowerTech OFS-3. This 3 bladed prop has a larger diameter, more cupping and rake, but 1" less pitch. If this works as planned, I should get the lift and "bite" I'm looking for as well as that 100rpm I'm down. The added R's "should" give me a bit more top end while the lower pitch giving me a little better hole shot.

I'm on a "exchange" program so if this doesn't work, it'll get swapped out until we find the Holy Grail of props for my boat. I may try that OFS-4 if this doesn't perform as expected. We'll see...

[Moose-Hunter]

A new prop is installed and waiting for water testing. I went with a PowerTech OFS-3. This 3 bladed prop has a larger diameter, more cupping and rake, but 1" less pitch. If this works as planned, I should get the lift and "bite" I'm looking for as well as that 100rpm I'm down. The added R's "should" give me a bit more top end while the lower pitch giving me a little better hole shot.

I'm on a "exchange" program so if this doesn't work, it'll get swapped out until we find the Holy Grail of props for my boat. I may try that OFS-4 if this doesn't perform as expected. We'll see...

This is the WRONG PROP for my application!!! IMHO... Not even close.

Although holeshot was slightly improved, most all other aspects of prop performance took a dive.

- As mentioned, hole shot slightly improved. Not anything to write home about that's for sure.

- Minimum planing speed actually increased. 20mph to plane, a couple more to make sure she stays on top. Up at least 3mph from stock.

- WOT rpm dropped 400. I was looking to gain only 100 to reach the magic 6K mark. Instead, I dropped to 5500 WOT trimmed to the max.

- As expected with a lower rpm, WOT top end speed dropped. A full 6mph!! I was tickling 47mph with the original Yamaha Reliance 19p prop. I could barely manage 41mph now with the same, if not a bit lighter load.

The Power Tech prop is a stout looking piece. Very easy on the eyes as well. BUT... This one ain't for me and it's going back on Monday. I'll try to get a different prop with the same pitch and diameter only a more cupped blade and possibly additional rake over the stocker.

Looked good on paper.... Real world testing told me different.

Back to the drawing board.

[boatfixer]

Really something messing with props and set up isnt it? Out west we did lots of high altitude testing with Mercury and Mercruiser. Fuel systems, props, gears, etc. Props had to be the most fun.

Good Luck with your testing and keep us informed

[Moose-Hunter]

Really something messing with props and set up isnt it? Out west we did lots of high altitude testing with Mercury and Mercruiser. Fuel systems, props, gears, etc. Props had to be the most fun.

Good Luck with your testing and keep us informed

Bruce, you aren't kidding!! There's so much more to prop performance than meets the eye. Black magic if ya ask me.

It was prop testing day at the lake. Had three props to compare to my stocker. It was kind of a pain, but I really made some headway.

First order of business was to get to that magical 6K mark on the tach. Easy... Either drop the pitch or a smaller diameter. We opted for the pitch change due to the larger 4.75" of the gear case. Much bettter prop selection in the pitch range we were looking at.

First to be tested was a 15 x 17 with very slight cupping in the blade. Hole shot was great! However, it took more MPH and R's to achieve and maintain minimum planing speed. Top end... Dismal. Only managed 40 and change wrapped tight at 6100+ rpm. This was the first time I ever hit a rev limiter on an outboard. Back to the box with this one.

Next was basically a 4 blade version of the prop mentioned above. The thinking was the added blade would hold better due to more surface area. Hole shot was very good. Typical of 4 bladed props. Planing was easy at lower rpm and speeds. Top end... 46mph and change. You could trim this one up 'til the cows came home. This would have been my choice if it weren't for two things... This prop chattered badly at idle (forward and reverse) and really low off idle speeds. Nothing that would hurt the engine, but way too annoying for me. Last... Either this prop was out of spec or the rumor about 4 bladed props being smooth is a myth. There was a noticable vibration until I trimmed out and powered up. THEN... it was smooth. Pass. To the box with ye!!

Last... another 3 blade. 1/2" larger diameter than stock, a 17 pitch with very cupped blades. Expecting about the same as the other 3 blade, I was pleasantly surprised!

Hole shot was great! Popped up on plane without the bow reaching for the sky. Got on top and planed out in about 3 seconds using only 16mph and about 2600rpm to stay there. Midrange punch was awesome! Went "hammer down" and really felt the acceleration. Top end... Same as the 4 bladed prop at 46 and change, reved out to 6100. All this with no weird vibration or chatter. AND... I got 4 blade performance with a prop that weighs a few pounds less. 11.6 for the 4 blade, 9.7 for this cupped 3 blade. Bonus! Decreased rotating mass = better fuel economy.

As mentioned, this is a 17 pitch. Rumor has it, this same prop is available in a 18 and a 19 pitch. My now slightly educated guess is that I'll end up with the 18 and run right at 5900 to 6000. Maybe even pick up a mph or two. I'm going to try the 19 pitch just for comparison sake to make sure there is not more to be had.

Todays testing was fun and quite educational. Not only am I getting a better feel for the "black magic" of prop selection, I now have launching and landing the new rig down to a science!

Oh yeah... All testing was done in a "to be fished" condition. As in ready to rock for two people for a day of rippin' lips. 1/2+ tank of gas, full front live well, fishing gear... and my "buddy" for today's tests was a pair of type 31 batteries strapped to the pedestal of the passenger chair. These actually outweigh my better have by 10lbs or so. (She made me say that. REALLY! )

Gotta run and clean these props off. As soon as I test the 18 and 19... I'll be back for (hopefully) a final update.

[boatfixer]

Hey that's awesome Dan! Glad to hear you you made headway and you learned a few things

[delmuts]

Sounds like you're very close to having the right set up for that boat! Testing props is a pain, and fun at the same time. Plus it is an education.( trust me on this! ) If and when you get a new/different rig you will have a much better idea of what you need and how to achieve it. The chatter with the four blade sounds suspicious! I went thru the testing process years ago with my 18 ft. ranger with a 175, and settled on a four blade. No chatter at any speeeds that i can remember! You will also have alot of satisfaction once you achieve the performance you want every time you're on the water.

[Sorgy]

Moose Hunter- who did you work with to get your props from for the testing. I have looked and had a hard time finding someone who will help out. You had someone great to work with. Even if you can just fire me a phone number that would be great.

Thanks

Steve

[Moose-Hunter]

Moose Hunter- who did you work with to get your props from for the testing. I have looked and had a hard time finding someone who will help out. You had someone great to work with. Even if you can just fire me a phone number that would be great.

Thanks

Steve

Hi Steve...

I've got a couple ideas for ya. Fire me off an email to moosehunter42 AT embarqmail DOT com.