hwsii Prop recommendation; merc 115 4 stroke

[duncc]

hwsii, I am following your procedure here for a prop recommendation (see my data below). I greatly appreciate your time.

I am wondering if I need a bow lift prop or a stern lift prop? I am looking at 4 blades now thinking some extra lift somewhere will help? I am not knowledgeable when it comes to boats.

I can get a solas titan 4 from local dealer, do you think this will help? Will it give me a better holeshot than the hustlers? Also if i go to 4-blade do i need to go to a different pitch as compared to a 3-blade? It seems like the 17P gets me in the right rpm range and gets me the top-speed but the holeshot is really poor. (I can't believe how gutless this 4-stroke feels.)

Iboats Boat and Motor Info
1. 2006 Lowe FS175 Fish and Ski
2. 17'-3" length, 80" bottom width, 92" beam, 1150 lb base weight
2a. 115 hp max
3. 3 people 10 gallons gas normally
4. Some fishing, some slalom skiing with 200 lb skier
5. Deep V not sure about dead rise
6. 2006 Mercury 115 4-stroke
7. 115 HP 2.07:1 gear ratio
8. 5000-6000 rpm WOT range
9. A/V plate 1" above bottom of keel
10. No pad bottom
11. No hydrafoil trim tabs etc.
12. Turning Point Hustler 15Pitch / TP Hustler 17P
13. 3 people in boat 10 gallons gas, 15P: 6000 rpm WOT (could rev more but I hold it back) 35 mph / 17P: 6000 rpm 40 mph (unfortunately not GPS)
14. 3900 ft elevation
15. Motor is all good 30 hrs on it
16. Have been trying props to get better holeshot for skiing
17. Props are brand new
18. Holeshot is terrible with 17P (cannot pull up skier), ok with 15 but still not great, top speed too low with 15P (too slow for skiing)


Thanks

 

[hwsiii]

Re: hwsii Prop recommendation; merc 115 4 stroke

Duncc, one of the reasons you are not getting the power you think you should is because you are at 4,000' Elevation, that means you are only getting about 101 HP out of your motor. The next problem you have is that your prop slip with the TP Hustlers is still rather high at 14%, as I believe you can raise the motor up one more notch on the transom and lower your prop slip some, but you will still need a better prop for skiing at that elevation.

Prop Slip

Also please take a couple of pictures of the anti ventilation plate with a straight edge and the the top of the motor at the transom, so I can see where the motor is positioned.

Ant Ventilation Plate

And my last question is do you run this boat at this elevation all of the time, and if not what other elevations do you run it at and how often.



H

 

[cloumar]

Re: hwsii Prop recommendation; merc 115 4 stroke

Hi duncc,

Your RPM range may not be right - if you have the new style Merc 4 stroke which is a block of a Verado with a gear ratio of 2.07 - your RPM range is 5800 - 6400 - I own a 2007 - 115-hp and it is a 2.07 gear ratio.

in 2006 I believe that there was a break somewhere and there is a production of the previous generation with a 2.33-gear ratio and the newest one with a 2.07 ratio

MC

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

MC, the motor is the old style 2006 with square hood; the WOT range is 5000-6000 and the gear ratio of all 115 4 strokes from 2001-current is 2.07:1.

hwsii, thanks for your help I really appreciate it. I have attached a couple of pics as you requested. Hopefully they are clear. The bottom of the level (straight-edge) is even with the top of the A/V plate.

Also, the boat will be primarily run at elevations between 3000-4000 ft, these are at the lakes we use the boat. About two weekends per year we will run the boat at sea level so our primary concern is at the elevation.

I thought that the EFI would compensate for elevation changes. Also, does the elevation affect prop slip? When you say I need a better prop for skiing can you suggest something? Is a 4-blade ideal for this?

Thanks again,
Duncan

 

[cloumar]

Re: hwsii Prop recommendation; merc 115 4 stroke

Sorry Duncc,

Your are right about gear ratio - my mistake

MC

 

[larry beckett]

Re: hwsii Prop recommendation; merc 115 4 stroke

Some very good information here. Once the motor is at the right height on the transom the prop is still a complicated issue. Perhaps I can humbly offer a couple of simple thoughts in just the area of the prop. Hard to get them just perfect. I note that you pull a big slalom skier. This takes some "stump pulling" power. You also like to be able to cruise at a reasonable speed. You'll probably wind up always with two props in order to get both worlds. However, you might want to see if there is a really good prop shop in your area. A guy who can tweak your prop to do what you want. If you have such a guy in your area he can add holeshot, lift or what ever you need. Such a guy will usually be well known to the local boaters. When I was into the faster boats I gave up on new props. Found that if I could find a clean used one close to what I needed I could get the local prop guru to make it work for me. Usually saved money and ultimately wound up with a very good prop.

 

[hwsiii]

Re: hwsii Prop recommendation; merc 115 4 stroke

Duncan, Mc is just trying to make sure that you have the right information about your motor. You wouldn't believe how many people come here with the WRONG information on their motor.
People do not realize how much difference there can be in the prop pitch needed to run at elevations above 3,000'. I am not positive about the changes when you are running an EFI, in my opinion it would depend on how the electronics and software are setup for each model of engine. Theoretically it could possibly be adjusted by the dealer for higher elevations, you might want to check with your Mercury dealer on this.
You say you are running at 6,000 RPM with the 17" Hustler at this time. In most cases I would recommend you buy a 17" pitch Solas Amita or Rubex for your motor and raise the engine up one more notch on the transom, but I am not positive that is going to give you enough hole shot at this time. I know all oft his is a pain for you, but I will ask you to move your motor up one more notch on the transom since you have a deep vee hull form. Would you also take another picture of the stern of the boat from about 2' behind the motor and level with the anti ventilation plate so i can get a better perspective of the amount of vee and the placement of the anti vent plate. After you do that I would also appreciate it if you take the boat out again and run it with only the 17" hustler so we can see if that does what I think it will, I expect you to gain some RPM and speed from doing this.
The Hustlers are excellent props, but in my opinion on Deep vees, especially when you are running 4 strokes, the amount of rake and cup they have can be a hindrance when you are running with heavier loads and trying to ski at higher elevations.

The following are some very close approximations of the HP curves for a Yamaha and Etec in two strokes and a Honda four stroke in 150 HP engines. If you will look at the flatter HP curve produced by the four stroke you can see why they aren't as strong as the two strokes.These are the only three HP curves I have except for a Vortec.

HP curves

To answer your other question about prop slip as well as cavitation, yes higher altitudes also decrease the temperature of the boiling point of water which means cavitation starts at lower RPM than it does at sea level, that is the same reason that when you cook foods at higher elevations the the temperatures used are different than at sea level. Also with the higher elevation and lower air pressure it is easier to have ventilation as well. There is another 2 pages I could write about how much differene there is as well when humidity changes at altitudes, but what I have said is enough for right now.

I KNOW all of this is a PAIN, but I am just trying to do the best job I can for you.


H

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

hwsii, this is fantastic information and i appreciate your thoroughness. I am a mechanical engineer myself and am very interested in figuring this out if possible, and if not, i may be willing to get a new motor.

This weekend i am salmon fishing off vancouver island, BC and the boat seems to run better at sea level, though the top speed is still way down. (32 mph on GPS with 15P.) Unfortunately I cannot adjust motor height right now, I will take more pictures for you etc. when i get home.

thanks
Duncan

 

[hwsiii]

Re: hwsii Prop recommendation; merc 115 4 stroke

I will be waiting for you Duncan.


H

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

I have attached pictures as requested for the current motor height. We initially did run the 17P hustler one hole higher (about 3/4" higher) than pictured as you suggested and got 43 mph at 6000 rpm. Holeshot improved a little over the current motor height (pictured) but was still not very impressive. We ran the 15P at the higher motor height as well but dropped it back down trying to lose some rpm.

I have larger, clearer versions of the pictures, but I had trouble uploading them here. I can email them to you if you like.

Thanks

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

I am also wondering if Smart tabs/trim tabs would be a good idea for this boat?

 

[hwsiii]

Re: hwsii Prop recommendation; merc 115 4 stroke

Duncan, I am sorry I don't know how I missed your last posting. The only thing I can guarantee that will give you a great hole shot is to buy the 15" pitch Solas 4 blade and raise the motor up one more notch on the transom. That will bring your speed up to at least 38 MPH and your top speed now is only 40 MPH with the 17" so that ought to work fine. The only thing you will have to be careful of is not over revving the motor. This is not the ideal situation, but it is the only way I KNOW you will have enough thrust to pull up skiers even when the boat is loaded down with extra gear and people.


H

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

Is there a particular Solas 4-blade model I should look at? Would you suggest steel or aluminum? In my experience steel props only provide minimal improvements over aluminum and don't justify the extra cost. (Plus it makes the motor really clunky when shifting in and out of gear.)

Also, what do you think about the smart tabs?

Thanks again
Duncan

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

Is there a particular Solas 4-blade model I should look at? Would you suggest steel or aluminum? In my experience steel props only provide minimal improvements over aluminum and don't justify the extra cost. (Plus it makes the motor really clunky when shifting in and out of gear.)

Also, what do you think about the smart tabs?

Thanks again
Duncan

 

[hwsiii]

Re: hwsii Prop recommendation; merc 115 4 stroke

Yes Duncan, the Solas Amita 4 blade in aluminum and we will wait on the smart tabs until we see what the Solas Amita does for you. And I agree with you that changing to SS in many cases only shows small MPH gains.


H

 

[duncc]

Re: hwsii Prop recommendation; merc 115 4 stroke

Ok.. thanks again for all your help with this, it may be some time before I get the prop and try it out. I'll be sure to let you know of my results.