Switching from Aluminum to SS

[Birdman84]

Looking for a little guidance on prop selection. I decided to switch to stainless because I mainly boat in the inter-coastal and do a lot of beaching for the family. My aluminum props eventually get dinged up from small objects in shallow waters. I have a 3 blade 14 x 17 pitch prop on a Johnson 90 2 stroke behind a 2006 Sea Hunt Triton 186. My current performance on a full tank of gas and 4 people on board is WOT 36MPH at 5300 RPM, pretty good for me but maybe would like another 1-2 hundred RPM increase. My hole shot is great. I've looked at the Power Tech which seem to have several choices but I know there's a lot others out there and a lot to consider. My current prop has fairly moderate rake and is semi-cleaver style. Would I be best going to a 17 pitch stainless, same style prop and be okay RPM-wise? Hate to make a $450 mistake. Thanks for any input.

 

[harringtondav]

If you are looking for engine RPM increase, you need to reduce your prop's pitch. But your performance sounds pretty darn good as is. The lower pitch will give you a better hole shot and increase your payload capacity, but your top speed will likely decrease. My opinion: SS prop just like you have, 14 x 17. And you can purchase this for much less than $450 if you shop around with Google.

 

[jimmbo]

Cleaver type Props,

if that is what you have, are not great props for recreational boating as they are Stern Lifters, That works well on Tunnel/Picklefork racing hulls as it helps keep the boat from flipping over backwards.

Since I don't know how the engine is mounted Height wise on your boat, you might be able to raise the engine using a higher performance SS. Also it may also may allow higher trim angles while running straight ahead. A 17" pitch would be a good place to start, but don't get your head up your behind if the diameter is slightly different, leave that worrying to the Prop Engineers. Props can make the boat feel and handle differently too. Props like the Raker and Enertia can lift the entire boat vertically, resulting in less drag and more speed. Your 90 hp actually makes its peak power a couple of hundred rpm below 5000. Maximum speed will be attained propping for about 4800 rpm, propping on either side will result in a slighly lower top speed. At rpms above 5500, the 90 is putting out less HP than it would at 5000 rpm due to the small intake and exhaust ports on the 90. Makes for great low Torque, but it just runs out of breath at higher rpms

$450 isn't too much money to spend on a SS, the three I have, average about $750 each, and are worth every penny.

 

[WesNewell]

A little less than $450 here. And you can find it for a little less than this.
https://www.iboats.com/shop/solas-n...n-3-blade-stainless-steel-boat-propeller.html

 

[dingbat]

My opinion: SS prop just like you have, 14 x 17. And you can purchase this for much less than $450 if you shop around with Google.

The better stainless props are “performance” props. Designed to address particular performance issues.

Buying a copy of your aluminum prop in stainless steel buys you nothing you but bling.

The money spent on my Enertia was money well spent from a performance stand point

 

[alldodge]

My aluminum props eventually get dinged up from small objects in shallow waters

Folks have you covered on the stainless but you might think a bit more about maybe keeping aluminum. The stainless won't ding as easy but also is harder on the drive if something is hit. Prop shops can fix an aluminum fairly cheap

 

[jimmbo]

Folks have you covered on the stainless but you might think a bit more about maybe keeping aluminum. The stainless won't ding as easy but also is harder on the drive if something is hit. Prop shops can fix an aluminum fairly cheap

First Impact with my SS, a RAKER, resulted in a damaged Prop, scratched Skeg, and a bent Prop Shaft. $$$$

 

[Sea Rider]

If in pursuit of a slight 100/200 wot rpm increase with same load send current 3 x 14 x 17 prop to a prop shop and have it repitched to 14 x 16.5. Half pitch decrease should put motor to rev around 5100, only checkable with a new wot test...

Happy Boating

 

[Birdman84]

Cleaver type Props,

if that is what you have, are not great props for recreational boating as they are Stern Lifters, That works well on Tunnel/Picklefork racing hulls as it helps keep the boat from flipping over backwards.

Since I don't know how the engine is mounted Height wise on your boat, you might be able to raise the engine using a higher performance SS. Also it may also may allow higher trim angles while running straight ahead. A 17" pitch would be a good place to start, but don't get your head up your behind if the diameter is slightly different, leave that worrying to the Prop Engineers. Props can make the boat feel and handle differently too. Props like the Raker and Enertia can lift the entire boat vertically, resulting in less drag and more speed. Your 90 hp actually makes its peak power a couple of hundred rpm below 5000. Maximum speed will be attained propping for about 4800 rpm, propping on either side will result in a slighly lower top speed. At rpms above 5500, the 90 is putting out less HP than it would at 5000 rpm due to the small intake and exhaust ports on the 90. Makes for great low Torque, but it just runs out of breath at higher rpms

$450 isn't too much money to spend on a SS, the three I have, average about $750 each, and are worth every penny.

Thanks jimmbo, sorry to hear about the damage from the prop strike. Good to know where my peak power is. Mine is that style but it's semi-cleaver, so not as fine of a tip, and slightly rounded on the trailing edge of the blades. I forgot to mention however that my aluminum blades are very thick, thicker than others I've owned in the past on other boats and is very heavy. I'm concerned that a stainless prop, same diam./ptich/style may increase RPM, and possibly more than I would like to. And from what you've stated I'm not sure I want much increase at all. I did just find out that PowerTech offers an exchange program if the prop doesn't fit the bill. In their words..."for a nominal fee". That leaves a lot to be questioned.

If you are looking for engine RPM increase, you need to reduce your prop's pitch. But your performance sounds pretty darn good as is. The lower pitch will give you a better hole shot and increase your payload capacity, but your top speed will likely decrease. My opinion: SS prop just like you have, 14 x 17. And you can purchase this for much less than $450 if you shop around with Google.

Thanks for the suggestion, I've been on/off the fence with the same thought, Maybe consider one that is not the cleaver style, something with more surface area on the blades but same size? Would I be pushing it to try a semi-cleaver 19 pitch? Not looking to reduce my hole shot much, a little would be okay. A little higher top end speed wouldn't be so bad either, as sometimes I am in a hurry down the waterway running from storms during the summer!

Not looking to re-work an aluminum prop I'd rather buy a new one, but don't deal with many rocks or stumps where I go so I'm not too concerned with the risks associated with SS props.

Thanks for all the input guys, I'll be sure to post performance results once I get this figured out


Happy boating everyone

 

[WesNewell]

If you're looking for a performance increase, the very first thing to check is engine mount height. If it's mounted too low it can cost you as much as a 20% decrease in speed and fuel economy. It will also reduce the rpm at wot because of the extra drag. Mounted at the proper height you may even need to go up in pitch. So check engine mounting before screwing with props.

 

[QBhoy]

Hi
a difficult one this. A cleaver type prop usually makes its own rules up to the standard rule of thumb base line of a normal prop.
Im thinking that 14” diameter is a pretty big prop to swing at 17” pitch. I’m guessing the average normal stainless prop for your boat would be usually no more than a 13-13.5” tops. That’s likely what’s dragging your rpm down too, cleaver are known to show a lower rpm at anything other than aired out, trimmed to the limit and on a performance hull. Hard to guess at how a normal prop would end up in terms of rpm in comparison.
I had a semi cleaver type ballistic prop on the boat for a while. Compared to a laser 2 the same pitch, it dropped the rpm all the way through the rev range, but equalled it or more when trimmed right out and air under the hull at over 60. Funny things.

 

[Birdman84]

I would say raising the motor is probably not in my future. When I'm trimmed up on plane, going through wakes or other disturbances in the water, it can occasionally cavitate forcing me to lower the throttle or trim down substantially before it retains it's bite, then bring it back up. I feel raising my motor would make this worse. The cavitation plate currently sits in line with the very bottom of the hull. May try to raise motor after SS replacement if no signs of cavitation.

QBhoy - I've gotta agree that 14" diameter seems a bit large for 17 pitch on my 90hp. Thanks for explaining the dynamics behind the cleaver style vs normal blade props, as intuition had me thinking that switching to a prop with more surface area would likely bring my RPM's down. I have laid my eyes on a 13.5 X 17 pitch Power Tech all around performance prop here is the link - http://www.ptprop.com/index.php?pag...facturer_id=0&option=com_virtuemart&Itemid=46, thinking I may test their exchange program should the prop not yield desired results.

Continuing my search for a day or so but will likely pull the trigger on the PowerTech. Will post results as to help anyone in a similar predicament. Thanks all, happy cruising.

 

[QBhoy]

I would say raising the motor is probably not in my future. When I'm trimmed up on plane, going through wakes or other disturbances in the water, it can occasionally cavitate forcing me to lower the throttle or trim down substantially before it retains it's bite, then bring it back up. I feel raising my motor would make this worse. The cavitation plate currently sits in line with the very bottom of the hull. May try to raise motor after SS replacement if no signs of cavitation.

QBhoy - I've gotta agree that 14" diameter seems a bit large for 17 pitch on my 90hp. Thanks for explaining the dynamics behind the cleaver style vs normal blade props, as intuition had me thinking that switching to a prop with more surface area would likely bring my RPM's down. I have laid my eyes on a 13.5 X 17 pitch Power Tech all around performance prop here is the link - http://www.ptprop.com/index.php?pag...facturer_id=0&option=com_virtuemart&Itemid=46, thinking I may test their exchange program should the prop not yield desired results.

Continuing my search for a day or so but will likely pull the trigger on the PowerTech. Will post results as to help anyone in a similar predicament. Thanks all, happy cruising.

Excellent stuff. Keen to hear how you go.