Was this a good choice?

[maharg]

I have a 16.5 foot runabout with a merc 3.0 140hp. I am currently running a 3 blade 17p prop and at wot I get 32mph. I just ordered the solas 4 blade 19p, I am hoping to be able to plane faster and get 35+mph. After all my research it seemed like the best way to go, agree or disagree.

Thanks

 

[steelespike]

Re: Was this a good choice?

You should read the stickies at the top of the page and the helps on the prop store page.
You shouldn't make any prop changes without a tach.We need to know your present
max rpm and speed
There is something wrong with your setup.A 17 should get up pretty easily. And run more than 32. Probably over reving at wot(wide open throttle)Your boat would noremally run about a 21" prop at over 40 mph.Most likely something is up with the motor.
Be sure the throttle plates in the carb open all the way,it is in excellent tune firing on all cylinders,good compression.Timing advancing as it should.

 

[maharg]

Re: Was this a good choice?

4400 gets me 32+/-

I read the stickies, I feel I made a decent decision< i just wanted to see if others agreed that I would be able to get 35 and plane out faster with the prop I opted for.


The boat currently planes quickly, but not until 25 or so. I read 4 blades plane at lower speeds. I have a 1yo son and I dont plan on going much over 20-25 with him aboard.

 

[steelespike]

Re: Was this a good choice?

If your at 4,400 at about 32 Your allready barely into the max rpm range with a 17.
by going to a 19 you will lose "about" 400 rpm by going to a 4 blade could lose "about" another 100. Your motor will be lugging.And probably lose speed.
You need to figeure out why it lacks power.
Boat motors work like they are going uphill all the time.They need to be propped near their max rpm range.You just put yours into overdrive.
Not trying to put down your choice just trying to make the facts clear.

 

[maharg]

Re: Was this a good choice?

I am sure I could go higher than 4400, I am not saying the motor was capped there. I dont want to take it higher, its a 23year old engine and I dont have $ to replace the motor.

Again, I did read all of the articles on this site as well as others.

 

[steelespike]

Re: Was this a good choice?

imo If you run the motor with the 19 you will shorten its life.
Going to the 19 pretty much eliminates any hole shot advantage from the 4 blade. Just the fact it is a 4 blade will reduce your max rpm.
adding 2 inches will take even more.Your opening post said wot 32 later said 4,400.then later you said 4400 was not wot.How can we make any sense out of your setup?Your motor needs to be propped to rev freely to its max rated rpm at wot.Theres no need to run it there run at what ever speed you feel comfortable.
Don't force the motor to operate outside its rated range with a prop selection.
I hope you prove me wrong and I hope all goes well.

 

[maharg]

Re: Was this a good choice?

The tag on the motor says WOT is 4400-4800, I didn't realize you meant the obtainable maximum rpm

 

[maharg]

Re: Was this a good choice?

I can return it for a different one, what would you advise?
The boat is 1750 dry weight
We usually carry 900sih lbs
I don't know what my true WOT is, I get to 4400 and don't push any more
The boat planes quickly, but It doesn't plane until 25
at 4400 I get 32ish mph
the prop is a 17x14.5 aluminum

I want to get 35mph at the same or lower rpm
I want the boat to plane at lower speeds (this is why I went 4 blade)

What should i go with?
I did the 4 blade 19 pitch because all of the prop calcs said that was what was closest to what I was looking for. I would have bought an 18p but there is not a solas 4 blade 18p and a 17p is what I already have.

Pardon my ignorance but I am a newbie.

 

[steelespike]

Re: Was this a good choice?

Now your talking. Unfortunately without your actual wot rpm and speed its reeally difficult to know where your at. If your motor is reasonably sound it isn't likely to fail for a minute or two at actual wot.I had a 70 year old boat that had never been rebuilt and had excellent care I routinely ran it wot for a minute or so just to excercize it.Without that info I would suggest a Solas Amita in a 17" it will give you
your hole shot and stay on plane with less power.May reduce your max rpm but you
could have some pitch removed to improve that.Also sometimes they remove a little cup to improve rpm.

 

[maharg]

Re: Was this a good choice?

I read that if I go with the same pitch but a 4 blade I will lose MPH. I would still like to hit 35@4400, when I used the prop calc tool it said a 19p will give 36 @ that rpm.

 

[steelespike]

Re: Was this a good choice?

Without knowing your present "actual" max rp[m and speed there is no way to know
if your motor can turn a 19.We don't even know for sure the 17 will reach max rpm. In order to turn a 19 it would have to be over reviung with the 17 To be at the correct rpm you would have to have an actual rpm of about 5,200 so the 19 X4 would drop your rpm "about" 4 to 500 rpm.
Understand the motor must be able to reach its actual rated max rpm at wot.
that way it will be at its ideal rpm whatever throttle you choose to run at.
You seldom can improve hole shot and speed on the same prop.
Its like expecting a car to go the same in high gear or 3rd gear.
By going with the 17 X 4 your only going to lose the rpm of going to a 4 blade.
By the way not all 4 blade results actually reduce speed.It depends on the previous props actual performance,the hull design and motor setup.Its intirely possible for the 4 blade to deliver the same or better speed.Again we are in the dark as far as your present actual performance.

 

[maharg]

Re: Was this a good choice?

Okay, I am Going to the river on Saturday and staying the night. Would you say 5200 rpm is minimum to go to the 19p? What if I hit 4800 or 5k? I will just take the prop with me and put it on depending on rpms I guess?

 

[steelespike]

Re: Was this a good choice?

I just noticed you said you carry about 900lbs.The 19 may not respond to that weight.But if your over 5,000 give it a try you'll have the prop anyway.
If you endup at say 4,600 with the 19 and then you add 900 lbs you'll probably drop out of the rpm range. If you typically run with about 900lbs it would be nice to endup within the range at least at the bottom rated with that load.
If your load performance is adaquate with the 17 I don't think you'll be happy with the 19. But I could be wrong.I thought I was wrong once but I was mistaken.lol
I noticed in another post you have a foil added it will get you on plane faster and may keep on plane at lower power but it will likely eat up your speed probably through mid to high speed.Economy in a boat depends on the most speed for the least throttle.
If you dragging the fin your losing speed. The 4 blade should help a lot if you need more consider something like Smart Tabs.Try the 4 blade without the foil.