Theretics of my new prop

[Philster]

Re: Theretics of my new prop

Ok, So im new to the boat world, got a 19' galaxy bowrider and a 1975 evinrude 85hp 13tooth spline

Ive been looking into the origional prop that came on the motor and it seams that it was a 13-3/4x23 and a 13-3/4x21

Ive spent about 6 months rebuilding the entire boat, new floor, transom, seats, dash, paint, and now the motor. Ive been reading about props and motors and unlike a car, the RPMs of the boat are what determine the speed, so my two questions?

1: If the speed in wich the prop turns and the pitch determins the speed in wich the boat travels, why do people boast a higher HP motor when they are just adding weight?

.

Quoted for a reminder of how this train wreck got started. You asked questions that were answered; refused to accept the answers, and are insulted we don't value your complete lack of boating experience in countering anything you offer out of your own lack of knowledge.

 

[steelespike]

Re: Theretics of my new prop

Your 150 leg is likely a 1.85 ratio.Your power head is as much as 130 hp.
I looked up 9 new 150s on boats ranging from 17ft to 22ft.mostly glass one aluminum average prop size was 17" with largest 19 smallest 16.
Speeds 39-48 mph rpm 5200 to5750. One vary fast =Checkmate 20 ft 1400 lbs had a 22" prop did 61 at 5500.
Take what you want from this but it doesn't appear a 23" will work.
Was your Galaxy originally an I/O? couldn't find a outboard.

 

[sublauxation]

Re: Theretics of my new prop

The cool thing about interchangeable hubs is that while you may waste $276.95 on a prop, that $40 hub can be used with any other Rubex prop.

 

[olivialyn11]

Re: Theretics of my new prop

Your 150 leg is likely a 1.85 ratio.Your power head is as much as 130 hp.
I looked up 9 new 150s on boats ranging from 17ft to 22ft.mostly glass one aluminum average prop size was 17" with largest 19 smallest 16.
Speeds 39-48 mph rpm 5200 to5750. One vary fast =Checkmate 20 ft 1400 lbs had a 22" prop did 61 at 5500.
Take what you want from this but it doesn't appear a 23" will work.
Was your Galaxy originally an I/O? couldn't find a outboard.

I couldnt find any other out boards either, when i bought the boat it was outboard.... i would have preferd inboard because its much eaiser to modify a regular engine block then a o/b motor. i only weight 1800lbs do you think if i could squeez a little more out of the motor a 19"4Blade would be to much, or just run a standerd 19? as long as i stay above 4500 the motor should hold out right? as long as we didnt mess up any machineing? its all balanced so im not really worried about a top rpm

 

[steelespike]

Re: Theretics of my new prop

I really think your better off with a 17" pitch.Keep in mind all the tests were 150 hp motors and the boat with a 19" prop was 1650
lbs and had a fast bottom ran at 48 mph @ 5450 fastest of the non Checkmate types.
To fully realize your hp you need to be able to reach close to your 5500 you had in your Dyno test.
I have a feeling your bottom is probably like a deep V.It will give a nice ride but not too fast.
If you do the 19 you might get into the low end of your range but will likely be sluggish. And won't have much reserve for loads or water sports.If you go with a 17 and it ends up a little light you can still use it and just watch the rpm.
If the 19 is over propped the motor will lugg and you shouldn't run it for extended time over a fast no wake speed.
You certainly could test it and use it while trying to fine tune the setup but over time lugging can cause premature motor problems.

 

[sublauxation]

Re: Theretics of my new prop

If you are anywhere near Minneapolis or Fox Valley WI I'd be more than happy to let you test with my 3 blade 17 pitch TP Hustler. Are there any prop shops nearby that will let you try them? Some are decent about it as long as you put the money down first. I know for fact there are a lot of decent 13 spline Evinrude props out there on EBAY in both 17 and 19 pitch. (I just put 13 in the search area and that weeds out most of what wont work) The 4 blades are harder to find. I bought a nice SS 15 pitch last spring for $50. Definitely stick with the interchangeable hub if possible if you go new.

 

[aerobat]

Re: Theretics of my new prop

The lower unit is off of a 1977 150hp
Uper unit is a heavly modified 1975 85hp prodicing around 120-130hp

gents, dont you get it that he is most probably joking us ? you make here a brain storming for something that is nonexistent.

please show us some pics of your heavily modified 85hp pushing now nearly 130hp . what did you installed ? a supercharger?

 

[Philster]

Re: Theretics of my new prop

I would like to see pics of how the engine (prop shaft and antiventilation AV plate) sit in relation to the bottom of the boat.

Putting the prop into dirty water by burying it even 1-3" will knock off some RPM.

Having it too high on a V bottom boat will kill bow lift. W/out bow lift, there is more wetted hull, which = drag.

Boats without a real serious V can simply err on the high side. The prop doesn't need to be low enough to produce bow lift. V-bottom boats don't have this luxury. They have a sweet spot, usually only 1 to 1.5" in height along a given range. For example: On a given V bottom boat, the prop shaft sitting 2" below the bottom might be perfect, whereas 3" below knocks off RPM/speed.

Given all the variables, I think this one needs to be cleared.

EDIT: at the end of the day, only running the boat on plane and looking at the lower unit to see where the AV plate sits in relation to the water matters. It should skim just at the surface (visible), w/ maybe a little splash going over it while under way at speed.

Also, since the OP seems to have speed tricks in mind, one trick on V-bottom outboards, to get even less wetted hull, is to add a setback bracket to the engine.

 

[olivialyn11]

Re: Theretics of my new prop

gents, dont you get it that he is most probably joking us ? you make here a brain storming for something that is nonexistent.

please show us some pics of your heavily modified 85hp pushing now nearly 130hp . what did you installed ? a supercharger?

no we milled out the sleves on the block and stuck larger pistons and sleves, it looks exactly like an 85, but has new rods and gears in the lower unit that we harvested form a 150

if we can eventually figure out a better exhaust system we might try to add a turbo... not sure because we would have to modify the fiberglass cover and probly part of the lower unit.

the same way my srock 119hp 4cylinder now pushes 400hp, with time and wasting money, got the power of a 130 motor with the weight of the 85, difference of 50hp with out the gain of 150lbs

I would like to see pics of how the engine (prop shaft and antiventilation AV plate) sit in relation to the bottom of the boat.

Putting the prop into dirty water by burying it even 1-3" will knock off some RPM.

Having it too high on a V bottom boat will kill bow lift. W/out bow lift, there is more wetted hull, which = drag.

Boats without a real serious V can simply err on the high side. The prop doesn't need to be low enough to produce bow lift. V-bottom boats don't have this luxury. They have a sweet spot, usually only 1 to 1.5" in height along a given range. For example: On a given V bottom boat, the prop shaft sitting 2" below the bottom might be perfect, whereas 3" below knocks off RPM/speed.

Given all the variables, I think this one needs to be cleared.

EDIT: at the end of the day, only running the boat on plane and looking at the lower unit to see where the AV plate sits in relation to the water matters. It should skim just at the surface (visible), w/ maybe a little splash going over it while under way at speed.

Also, since the OP seems to have speed tricks in mind, one trick on V-bottom outboards, to get even less wetted hull, is to add a setback bracket to the engine.

my goal is to get the motor mounted in the next 3 weeks, just finished re-glassing the boat and are prepping for paint, not sure what an av plate is but as soon as we get the alumium mounted to the transom and the motor hung ill let you know how far the unit sticks out.... i also came across a free bee prop its a 13-1/4x17 and its in near mint condish so i can probly use it for a test run as long as its the right shaft size havnt checked it yet...

 

[BonairII]

Re: Theretics of my new prop

for all purposes the 85hp motor currently has 120 raw hp at the crank...

My guess is that the 85hp is getting 70-75hp at the prop(depending on how tired the motor is).

I've only skimmed this thread(the car talk got me derailed), but I'm guessing a 17pitch is probably a good starting point. You need an accurate tach on your motor to make ANY kind of educated decision on what prop to run.

Your motor has 10hp more than my '77 75hp motor...and you're boat is prob quite a bit heavier than my 16' fiberglass. I'm running a 17pitch and getting 5500rpm.

If you're loaded heavy, you may end up needing a 15pitch.

Keeping your RPM within the manufacturers operating range is very important....if you over-prop, you'll be lugging your motor.