How much of a pitch change do I need?

[QBhoy]

I spent the week on the water after raising my engine one hole. I did gain a couple hundred RPM and 1.5 mph but at the expense of blowing out while cornering. When I trim the motor down enough to prevent blowouts I’m back to exactly the same RPM and actually lower speed because the boat has to be trimmed so more of the pad is in the water. It appears the issue wasn’t motor height after all and I really do need a different prop.

I’m going to lower it back to where it was.

It’s pretty standard to have to trim down a little to corner at full throttle. Jeez with one of my boats, I if I didn’t trim down and slow down a little from full throttle, I’d end up in hospital for sure.

 

[Sea Rider]

That's why was highly suggesting to test the combo with motor sitting even on the transom, but you preferred going the other way raising it one hole which proved counter productive when boating at tight close corners at speed....I'll bet that if testing the combo as suggested will achieve no prop aeration along no trimming down under such condition.

The only problem that could encounter if the lower leg sits to low while the motor sits even on transom is a water splash produced side or out transom due to the flow hitting hard at speed above the lower splash plate due to its odd shape.

Happy Boating

 

[Elkins45]

That's why was highly suggesting to test the combo with motor sitting even on the transom, but you preferred going the other way raising it one hole which proved counter productive when boating at tight close corners at speed....I'll bet that if testing the combo as suggested will achieve no prop aeration along no trimming down under such condition.

it was easier to raise it than it was to take someone with me to drive while I looked.

I’m confused by the rest of your post. “Testing the combo as suggested” is basically just running it as-is.

 

[Faztbullet]

If your prop is designed like this you need to go to a round ear prop with cup and raise engine back up 1 hole..

 

[Sea Rider]

it was easier to raise it than it was to take someone with me to drive while I looked.

I’m confused by the rest of your post. “Testing the combo as suggested” is basically just running it as-is.

Yep, the issue is that if you don't test what's going on at back transom while someone looks down won't know for sure at which lower leg the hardened water flow will pass by and that's essential to figure it out. Wot water tests should start with motor sitting even on transom and then go from there...

The posted prop is the standard Yam prop I've seen in all Yam motors up to 120 HP ones, Yam knows their prop business well, my friend's Yam motors not running top only required buying same prop model in 1-2 less pitch size and fine tuning the motor height for water flow to skim right under the upper splash plate as in the posted example, that's the sweet motor height for yam motors to run top in All water conditions. BTW the 50 HP Yam motors has taller lower leg plates distance compared to Merc ones which are way shorter. What works top for one will not work same for the other..

Sit back the motor where it used to be, make a new wot water test as suggested along a rear spotter to check what's going on at back transom as blindly guessing, ear RPM taching is No Bueno and counterproductive. Dry installations along posted motor height pics doesn't say a word to me...seems for the rest is all to have in consideration.

Happy Boating

 

[Elkins45]

I already know what it’s doing at the old position. It’s running a 4400 rpm at wot. Raising it didn’t really make an improvement. That tells me that I really do need a lower pitch.

Having someone observe the water flow does nothing to change performance.

 

[Sea Rider]

Let me tell you from plain experience that if the motor achieves lower leg drag as explained in post 42 along being under propped there will be way more wot rpm reduction than if its only an under propped condition.

Anyway, according to post # 40 you were going to lower the motor as it was before, No one disputes that you don't need to change propeller, you do, the issue is how many less pitch sizes and which prop model will you need for the motor to rev to 5 K which is the wot rpm you were after..

Expect to receive theoretical varied answers along dumping money in the intent to better current performance, whichever pitch size and prop model you go for will need to be water tested. If not keep boating as you've been doing so far and as the french say,voila!!

Happy Boating

 

[Elkins45]

Let me tell you from plain experience that if the motor achieves lower leg drag as explained in post 42 along being under propped there will be way more wot rpm reduction than if its only an under propped condition.

Anyway, according to post # 40 you were going to lower the motor as it was before, No one disputes that you don't need to change propeller, you do, the issue is how many less pitch sizes and which prop model will you need for the motor to rev to 5 K which is the wot rpm you were after..

Expect to receive theoretical varied answers along dumping money in the intent to better current performance, whichever pitch size and prop model you go for will need to be water tested. If not keep boating as you've been doing so far and as the french say,voila!!

Happy Boating

I had sort of hung my hopes on raising the motor as being a solution in and of itself. That obviously was not the case. Since I have to get a different prop anyway there’s no extra cost with leaving it raised when I mount the new prop for the first trial. If I have issues then it’s no additional cost to drop it back down.

The current prop is a 15 pitch. I’m going to substitute a 12 or 13 just depending on which I can source easier/cheaper. If I don’t make it to 5K then it will likely be close enough to be worth the effort. I need a spare prop anyway.

It’s a shame someone local doesn’t have a prop rental service, like trying on a shirt before you buy it.

 

[Faztbullet]

Get a Sola Amita with cup in 13 pitch.

 

[Elkins45]

Get a Sola Amita with cup in 13 pitch.

I really need stainless because I spend a lot of time idling thru submerged timber. Is there a stainless model? I didn’t see one with similar specs where I found the Amita. I found a Michigan Wheel Apollo in 10.5-13 that should fit.

 

[WesNewell]

http://solaspropellers.com/index.php/component/zoo/category/solas-brand?f=1&Itemid=144

 

[Sea Rider]

Your current wot rpm at 4400 rpm is 600 rpm far away from the middle yam parameter which is 5000 and 1100 rpm from the max which is 5500. Preferibly go for the max range if possible, motor will achieve a faster hole shot, trasport more load, along better fuel consumption at way reduced throttle as from right now.

As the post got long, don't plan reading it all again, don't know if it was stated before : Check that the throttle on the control box when at max forward position opens fully the butterflies in all 3 carbs. If out of adjustment along boating under propped expect a huge wot rpm reduction...

Happy Boating

 

[WesNewell]

A 15P prop is not too much for your light boat with only you in it. If you're on ly getting 4400 rpm, you've got other problems. Going to a 13P may bring your rpm up, but it's not going to fix the real problem.

 

[Elkins45]

A 15P prop is not too much for your light boat with only you in it. If you're on ly getting 4400 rpm, you've got other problems. Going to a 13P may bring your rpm up, but it's not going to fix the real problem.

I really don’t think that’s the case. Everything on the motor checks out is being 100% functional.

 

[WesNewell]

Look at post #6. That recommends a 16+ pitch prop for your setup for max performance. You're only getting 4400 rpm with your 15p prop. That's a 21% slip. And that's not good. Good is under 10%. It's not that hard to get down to 5%. So the reality is you've got a problem. Either your engine is crap, your hull is crap, your mount height is crap, your prop is crap, there's something else applying a lot of drag, or a combination of all these. One thing it isn't is the pitch. You should not need anything less than a 15p prop, and if you do, you will just be compensating for the real problems to get your rpms up.

 

[WesNewell]

My mistake. Assume this is your boat. 15.45 pitch prop is recommended with 300# people and gear. if this isn't what you have, then disregard. [h=3]Your setup[/h]

• Boat type: Rigid Inflatable
• Usage: Overall good performance/0 ft
• Engine Manufacturer:
  Yamaha
• Engine Type: Outboard
• Engine Year: 2003
• Number of Engines: One
• Engine Family: 3 Cyl 2-Stroke
• Engine: 50
• Drive / Gear Case: Yamaha 25-50 hp 2S, 40-60 hp 4S 1.85 Ratio

[h=3]Details[/h]

• Calculated Pitch: 15.45
• Calculated Weight with engine(s): 1,348.20 lbs
• Calculated Engine RPM: 5,000
• Calculated Boat Speed: 37.19 mph

 

[Sea Rider]

Holly guacamole, the whole dry troubleshooting is crap. What the prop selector recommends is only a reference to go for to choose a first starter prop if the current motor doesn't count with one, if does, then wot test it and go from there fine tuning your middle or max wot rpm range which one you prefer the most as this setting is not cast on stone.

Prop calculator "calculated" data will eventually vary when water testing, boat's hull can have more or less coefficient of drag, doesn't matter if being same size, same model manufactured by different boat brands.

The OP has not been much cooperative finding a solution for his problem, has not checked motor/transom height, if all 3 carbs are opening fully their butterflies when the control box is at max throttle position, if with a spun prop or on its way to become fully spun. These 3 issues will reduce any wot rpm achieved, add a over propped condition and will blow by far what the prop calculator calculated...

Happy Boating

 

[Elkins45]

Look at post #6. That recommends a 16+ pitch prop for your setup for max performance. You're only getting 4400 rpm with your 15p prop. That's a 21% slip. And that's not good. Good is under 10%. It's not that hard to get down to 5%. So the reality is you've got a problem. Either your engine is crap, your hull is crap, your mount height is crap, your prop is crap, there's something else applying a lot of drag, or a combination of all these. One thing it isn't is the pitch. You should not need anything less than a 15p prop, and if you do, you will just be compensating for the real problems to get your rpms up.

Both Solas and Michigan Wheel recommend a 12 pitch when I use their tools.

 

[WesNewell]

IF you have an inflatable hull, that may be right. It's my understanding that the G three V167C is a aluminum hulled inflatable from the iboats specs. Sure looks like an aluminum hull in your photo. If it's not, then that's the difference. And Solas prop finder doesn't list a rigid inflatable. The merc prop finder does.

 

[Faztbullet]

It not a inflatable!!!!!! Should hace the G series not K prop and a 12-13 pitch