need new prop help

[briboat]

I have a 2004 Silverline ls1700 fiberglass bowrider 2008 Mercury 115elpt 4stroke,2.07:1 ratio.The boat has 14degree deadrise 21 gal tank and approx 2000Lbs +500Lbs for load.I experienced porpoising with almost no trim so added smart tabs which has reduced. Looking to replace prop after lowering motor 1 hole it helped with porpoising but reduced wot to 5400 .
current specs with 17p and dealer loaned 15 p black max aluminum 3 blade

RPM 17pitch 15pitch
3200 17 pitch- 20miles 15p- n/a
3500 17 p -23 15p 20
4000 17p -28 15p 23
4500 17p -34 15p 29
5000 17p -39 15p 33
5400 17p -42
5500 17p max 15p 38
6000 17p n/a 15p 43
6100 17p n/a 15p 44 max speed all readings are using speedometer ,sorry no gps
general purpose is to reduce porpoising, day cruising with tubing(watersports),normally 3-4 people boat and occassionally 2 tubers,holeshot is ok with 17 p 3 people,was much better with 15 p but seem to cavitate, vent and slip on hard acceleration.
Open to using stainless or 4 blade .
Any suggestions would be appreciated .Thanks Brian

 

[steelespike]

Re: need new prop help

I think lowering the motor simply lowered the speed thus less sensitive to porpoising.hwsiii should be along with some selection help.
If your interested in a ss prop you might check out the turning point hustler.
ss performance at al prices.If you have porpoising at low trim you may need to move some weight forward.The Hustler will allow more motor height with
less ventilation(cavitation).

 

[briboat]

Re: need new prop help

Thanks for the reply,yes lost about 5 mph by dropping motor, was around 50-51 mph and rpm was good around 6000rpm before lowering dealer suggested lowering engine because trim could not be used and chine walking and porpoising easily at that height.Would be at point where it could not be controlled and felt dangerous. Old set up was dog out hole with 19 p and dropped to 17p. Now chine walk is gone but porpoised,added tabs allows trim of motor to 1/8 gauge then porpoising returns but can trim back down to reduce. High speed is not goal, good performance and watersports with 10yr old is goal.
Any further reply are appreciated. Thanks

 

[hwsiii]

Re: need new prop help

Bri, anytime the motor is raised the fulcrum point of the propeller and motor is moved up in the water column which will either help a higher raked prop to hold the bow up better or if the prop doesn't have enough rake and/or blade surface area it will cause the porpoising to get worse than it was before. Like Spike said some of the time moving weight around in the boat can help with porpoising at times. The center of lift moving back and forth from the center of gravity is what causes porpoising, trim tabs usually can cure this problem, but it appears in your case it didn't.
I would like you to take a couple of pictures of the boat with a straightedge or piece of straight wood under the keel with the anti ventilation plate parallel with the bottom of the boat and the wood showing under the anti ventilation plate so I can see how high the plate is in relation to the keel. Take the pictures from the side at keel level if possible and one from the stern as well.

After I have this I will be able to make a recommendation as to a better prop for your boat. I enclosed a picture to show you what I need.

Anti Ventilation Plate Height

H

 

[briboat]

Re: need new prop help

Having trouble uploading pictures,will try to resize tomorrow any help would be appreciated ,used canon camera can i transfer directly .Vent plate is 1/2 inch higher than bottom surface of boat .

 

[briboat]

Re: need new prop help-pictures for hwsiii

Re: need new prop help-pictures for hwsiii

I took these photo hope they will help you.Sorry boats in garage if need clearer photos can try outside on weekend. Thanks for waiting .
The vent plate is about 1/2 inch higher than boat bottom presently.

 

[hwsiii]

Re: need new prop help

Brian, you need to move your motor back up and buy this prop here at Iboats, it is a Solas Amita 4 blade and it will carry heavy loads and will stop your porpoising and jerk skiers up in a heartbeat.



Price: $98.99 You Save: $37.01 Compare: $136.00 Discount: 27.3% Off

Propeller Specifications:

SKU:#1413-130-15
Manufacturer: Solas
Brand: Amita
Material: Aluminum
Diameter: 13?
Pitch: 15?
Blades: 4
Rotation: Standard (Clockwise)

Usually Ships Within: 1 Business Day


H

 

[hwsiii]

Re: need new prop help

Brian, you need to move your motor back up and buy this prop here at Iboats, it is a Solas Amita 4 blade and it will carry heavy loads and will stop your porpoising and jerk skiers up in a heartbeat.



Price: $98.99 You Save: $37.01 Compare: $136.00 Discount: 27.3% Off

Propeller Specifications:

SKU:#1413-130-15
Manufacturer: Solas
Brand: Amita
Material: Aluminum
Diameter: 13?
Pitch: 15?
Blades: 4
Rotation: Standard (Clockwise)

Usually Ships Within: 1 Business Day


H

 

[briboat]

Re: need new prop help

Thanks hwsiii, when I calculated boat weight I added motor weight in,1200lb boat,450 lb motor, +fuel and equipment,500lb for passengers.
If your suggesting lifting motor back up would that prop still be correct.I beleive I was close to 6000 rpm before with 17 pitch but boat got too HAIRY to handle with porpoising and chine walk and 50 miles on speedo,so I never really got to do any testing.Motor was lowered over winter and tabs added after 2 nd run becuase slight porpoising was still there.Boat is new to me last year and had 2004 115 yamaha four stroke owner transfered to his new boat.Dealer said no issues known from previous owner.
And would this prop work at current engine height and why are recommending lifting engine back to middle hole.

 

[hwsiii]

Re: need new prop help

Brian, you are correct, I forgot your RPM were at 6,000 RPM before. Leave the motor where it is and just get the Amita 15" pitch 4 blade. It will raise the RPM up to about 5,800 RPM and you will feel no porpoising. It will not ventilate, you will not feel it slipping, it will be a much smoother ride and the hole shot and acceleration will increase a lot.
I work a lot with people who want the highest speed and that is why I reommended raising the motor. Good performance and great for watersports will be what you get. But you don't need to raise it.


H

 

[briboat]

Re: need new prop help

Thanks for the help,ordered the solas 4 blade prop,will post results next week.

 

[hwsiii]

Re: need new prop help

I will be waiting Brian.


H

 

[briboat]

Re: need new prop help

Thanks hwsiii,
Ordered prop locally and dealer did not have amita,he said the solas rubex 4 was the exact same blade except for the hub.
Very pleased with result.The boat snaps out water, and pulls tube like it not even there.Was even able to have couple kids in boat and 2 on tube.
Sorry will try to post more specs but here are a few.Lake was choppy and only got out to take kids tubing.
RUBEX 4 BLADE 15 pitch.
4000rpm 23 mph
6000rpm 44mph
It holds in tighter turns,hole shot to plain excellent,no venting on turns.

 

[hwsiii]

Re: need new prop help

I am glad it worked out well for you.



H