swapped Solas 4blade aluminum to 4blade SS

[bsaylors]

Hopefully somebody will know how to make the conversion and save me some $$ trying to find the correct pitch.
To start off, the boat is a 98 Crownline 2250BR w/5.7GSi
I bought an assortment of Solas aluminum props to find the 14x21 4 blade operated in the correct WOT range. After striking something and folding back a couple of the blades I decided to make the move to SS thinking if I stayed with the same brand I would use the same pitch prop. The SS prop has soo much more bite than the aluminum that I can only get 3400 rpm with full tank of gas, trim all the way down and only two people in the boat whereas I was turning 1000 more rpm with the aluminum with the same conditions

Long way of asking the question. Is there anyway to determine the equivilent pitch in the SS prop that would match up to the aluminum prop within the Solas line ? Or am I destined to trial/error based on lake test and monitoring the WOT rpms ?

As a side note, the boat runs 50mph with a little trim while only turning 3600rpm and the SS does much better with keeping the boat steady. Much better rde, imo.

 

[craze1cars]

Re: swapped Solas 4blade aluminum to 4blade SS

Your RPMs while trimmed full down is a rather meaningless figure. Your aluminum was slipping real bad in those types of conditions because the bow was plowing water, which loads the entire drive system unnecessarily, flexes and effectively flattens out the soft/weak aluminum blades a bit and reduces the prop's pitch while it is under that kind of load. So it spins faster due to the slip created. In comparison, the stainless prop under that same bow plowing driving condition simply CAN'T flex & therefore cannot slip like an aluminum in those same loaded conditions, because it's stronger, and it therefore maintains its pitch and grabs the water so much better. This is exactly how most stainless props save people gas compared to aluminum. They will push the boat at the same speed at much lower RPMS...because they have better bite and less flex.

Even your 50 mph stat "with a litle trim" is rather meaningless as well. Was this absolute full speed/wide open throttle/max trim? Or was there more to be had? If you trimmed up farther, would your speed and RPMS continue to climb? I would guess yes.

Basically you need to get much more active with your trim button in daily driving....and ESPECIALLY for correct prop selection. What we need to know to answer your question is: Your speed (GPS preferred), and exactly how many rpms it spins on each prop (but especially the new stainless), while at full top speed, wide open throttle, and trimmed out as far as humanly possible....just BARELY below the threshhold of the prop blowing out of the water and your rpms shooting thru the roof while speed drops...those are the figures that correct prop selection is based on.

It is quite common to need to reduce pitch when changing prop materials from aluminum to stainless, rule of thumb is generally 1" to 2" less pitch. But that only works if you had perfect RPMS to start with. Most often buying the exact same pitch in a stainless does not work well, as you are now experiencing.

If you share all your full speed/trimmed out run stats we can certainly help you get closer to where you should be.

 

[bsaylors]

Re: swapped Solas 4blade aluminum to 4blade SS

The Solas 4 blade aluminum 14x21 seemed to run right at the recommended range. WOT around 4800 (Volvo states range should be between 4600-5000) trimmed up with a speed right at 50mph.

New Solas 4 blade SS 14x21 (with a full 55gal tank) trimmed up was only able to turn between 3600-3800 rpm and running a tad over 50mph. Again it is a huge inprovement in ride, amazing how much better bite the SS prop has.

I went ahead and ordered the Solas SS 14x19 four blade, don't want to sit on the sidelines this weekend and have my fingers crossed it is enough drop in pitch to bring the rpms up. I'm a little concerned the 19 might a bit too much and the next step down, the 17, won't be enough prop. Hopefully as the gas tank lightens up the rpm will come into the desired range.

 

[craze1cars]

Re: swapped Solas 4blade aluminum to 4blade SS

Well, based on your numbers above, your original 4 blade prop had 22% slip. And your replacement prop had 0% slip (though if I add an inch for cupping, you get single digit slip).

If you're 1,200 rpms short of wehre you should be with the stainless, then conventional wisdom says you need to lose about 6" of pitch. Buying the 19 won't get you there, if you're buying an identical model. But maybe you'll get lucky if you get the motor up closer into its powerband and the horsepower will take over to help push it up into the range...

Methinks you'll proabably need the 17. Mail-order test-drives with stainless props can get very expensive....

Which model of stainless Solas 4 blade are you buying?

 

[bsaylors]

Re: swapped Solas 4blade aluminum to 4blade SS

Going from a 4 blade Amita , to the 4 blade Titan.
I totaly agree with both your comments, it is getting very expensive test driving props from iBoats. I should get some kind of fequent buyer points. I have a 19, 23 and 21 aluminum versions and this will be my second new SS prop (and one rebuilt from the marina).
With the old rule of thumb of 200rpm for each inch of pitch the 17 seems to be the right prop however, I haven't found anybody running a prop that small with a 280hp / 22' boat. I'll find out this weekend .
Worst case I have yet another prop to list on eBay

 

[Tail_Gunner]

Re: swapped Solas 4blade aluminum to 4blade SS

Well lets start from the top........


""As a side note, the boat runs 50mph with a little trim while only turning 3600rpm and the SS does much better with keeping the boat steady. Much better rde, imo"""


.

That is not possible it did not happen...Was a gps unit used to verify that speed??? If so your tach is badly off the mark..Have it checked out and see if it is accurate within 100 rpm from 800 to 5000 rpm....boat tachs look nice but they have a reputation worse than any fishing story..

Post the gearing on your outdrive it is stamped on the back...it sounds like your close to the right prop....you just need a accurate reading from that tach

 

[SparkieBoat]

Re: swapped Solas 4blade aluminum to 4blade SS

looks like you need a 4 blade SS 15 pitch prop to me. that should put you in the 4800 rpm range...I am assuming that you have no other issues with your set up, you also may want to consider trim tabs, which will lift the transom up some and create less drag, possiblly raising your RPMs. trim tabs are a very worth while investment. If it was my boat I would install trim tabs first then prop for 4800 RPMs.