Need higher pitch: how do I determine how much higher?

[Incorrigible]

Engine is a 1991 Johnson J225TXESS -

Two of them on a 29' Scarab Sport

The current props are three blade stainless steel. 20" pitch. Assuming they are Johnson Props (based on memory)

Full throttle hits the rev limiters.

The boat went through a major renovation and the weight reduction was significant.

Any thoughts on HOW to determine the best props for this application will be greatly appreciated.

I was directed here after posting similar on another page in this forum. It was suggested that engine HEIGHT (????) might also be an issue. Mind you, this is my first time setting up outboards.

GREATLY appreciated.

 

[Silvertip]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

You start by reading the READ THIS FIRST sticky at the very top of this forum.

 

[Incorrigible]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Sorry, thought that I had and answered those questions to the best of my ability. I'll retry:

1) Engine speed exceeds manufacturers recommended range when throttles set to WOT
2) Johnson. Factory? 3-blade. Stainless Steel
3) 14" diameter. 20" pitch
4) WOT RPM 6700 approx: Hitting rev limiter
5) Johnson J225TXESS. Translation: Johnson. J225TXESS. 1990. 225hp Two each.
6) Wellcraft. Scarab Sport. Mid-eighties. 29'. Weight unknown.

Trying to determine how much higher on the pitch I should go without resorting to trial and error.

 

[Incorrigible]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

....found a number of prop pitch calculators on line that were able to answer my question directly. Recommend anyone looking for pitch calculations turn to the calculators as your source for information.

 

[Robbabob]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Like to hear what you came up with. Are you going to a 24P?

Good luck!

 

[steelespike]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Prop calculators can be a big help; just keep in mind they are only as accurate as the input.

 

[Kiss4afrog]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

....found a number of prop pitch calculators on line that were able to answer my question directly. Recommend anyone looking for pitch calculations turn to the calculators as your source for information.

Can you post a link to the ones you found, used ?

 

[Robbabob]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Can you post a link to the ones you found, used ?

Just a matter of looking them up:

http://www.hillpropellers.com/propcalc.html

http://www.rbbi.com/folders/prop/propcalc.htm

http://www.watercraftservices.com/Propwiz.php?pageID=info_articles.php&article_number=2

 

[Silvertip]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

The problem with prop calcualtors is that those who don't understand the physics involved with propellers and engines, is that they play with numbers and soon learn that if they stick a 24P prop on a 15 HP engine they can go 60 miles per hour. They don't understand that it takes power to actually twist a 24P prop and engines in the 100+ HP range can have trouble twisting them.

 

[Port Monster]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Here is an anaysis I did on another site for scarab sport propping. Maybe it will give you some ideas! I am turning 23P blades now. I do not get to the rev limiter even with a light load. But, you are going to have to compare your LU gear ratio with mine and the rest below!

Billr302 - 2000 Scarab Sport w/ Evinrude 225's - 3 blade OMC 21P. After Bill's comments (see below) his RPM's are too high with the 21P and he is going to experiment with a 23P Mercury Mirage Plus. I do not know the differences with the gear ratio between his Evinrude 225 and the Mercury 225 EFI that I run but I suspect the different results with blades is a function of gearing.

NCBrewster - 1988 Scarab Sport w/ Merc 225 EFI's - Mercury Mirage 21P

ScarabChris - 1994 Scarab Sport w/ 250 Evinrudes - Mercury Bravo 1 4 blade 22P. After hearing from Chris (see below) he uses the 4 blade as it allows him to stay on plane at much lower speeds (giving him greater control of the boat when the sea conditions demand) and gives him a much better hole shot. The 4 blade allows him to stay hooked in rough water better than the 3, the fuel economy has improved and while a little has been taken off of the top end speed the benefits of the 4 blade outweigh this slight decrease.

ScarabMick - 2001 Scarab Super Sport w/ Evenrude E-tech 300's - Cyclone 4 blade 23P

TC Goldman - 1999 Scarab Sport w/ 250 Ocean Runners - Mirage Plus 23P

demjjm - ???? Scarab Sport w. Merc 250 EFI's - Mirage 23P

Markt111 - 94 Scarab Sport w/ Johnson 250 v-8's - No prop info provided

evinrude 225s stock 15 dia X17 pitch 5600rpm

Crabbie ole Fart - 88 Scarab Sport - Evinrude 225's - Stock prop 15 dia X17 pitch 5600rpm. Current prop - 4 blades 14.75 X15 5500 rpm. Reason for switch to 4 blade - but what a lighting hole shot. 4 divers x12 tanks for offshore is whyI swithed to 4 blades now runs on plane at 14 mph which is good in rough as hell seas. had to slam to plane w/3 blades in the rough water @ 18 mph and all the load

So the folks with 225's appear to be running 21P 3 blades. Those that went to 4 blade do it for better control in rough seas as they can operate the boat slower on plane, Ability to get on plane faster particularly if you are carrying heavier loads, limited slip in rough seas as the 4 blade stays hooked much better and better overall MPG with a slight loss of maximum speed. If I went to a four blade I assume that means I should drop down to a 20P? Does anyone else have any other input here?? Please!

 

[sschefer]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

Prop selection is somehting on the order of Black Magic, even the best of the best rarely get it right the first time. The calculators will get you in the ball park and then you need start playing to get max performance. If you want to step up to the plate then you need to stop looking at these stock props and step up into a perfomance prop like the Merc racing props or Mazco's.

If you're set on using off the shelf stuff then keep it simple. The Merc Mirage is a great prop and will kick you out about 200-250 rpms per inch of pitch. Try to stay within about an 1" of max diameter so you have some room to play there also.

The first thing you need to do is get it off the rev limiters so you really know where you are. Have those motors been worked over at all or are they stock? I suspect stock since they still have the rev limiters on them.

Are they canted in or canted out. If they're canted in you may be running in dirty water and cavitating your way to the 6700 rpm limiter. There are all sorts of tricks with twins that you need to research if you haven't already.

 

[Incorrigible]

Re: Prop Pitch - Where do I start

Re: Prop Pitch - Where do I start

"Worked over"? I'm intrigued. Tell me more. Some good advice here. (appreciate actually hearing someone admit that it's on the "order of Black Magic" for once)

Do you have any suggestions or recommendations on researching potential tricks with twins? Very interested.

Again, thanks....