volvo prop

[redbull1]

hi there just wondering what prop i should have on my boat. Boat is mainly used for fishing. Bought the boat with a 21 pitch but seemed to high. The boat is an 18' lund aluminum hull, 135 hp 3.0 litre 4 cylinder with an volvo penta sx out drive 1.87 gear ratio. Thanks

 

[hwsiii]

Re: volvo prop

Redbull1, we will try to help you as much as we can, but there is certain information that is needed in order to help you. The following form has all of the information that is needed to help you with your problems in finding the right prop. If you do not know all of the information that is asked for on the form please give us the most information you have available as I have a program I designed to find the right prop for any planing hull boat that needs this information, and most other people who are trying to help you will need the same information. It requires time to find all this information when we have to look for it and in my defense I expect you to be willing to expend as much effort in finding the right prop as I do. We hope to be able to help you get the exact prop you need for your particular uses, and this information is required to do that.
It is not as simple to pick the right prop as most people coming to this forum think it is, that is why we ask so many questions, it is for your benefit we ask all these questions. And if you have a stainless steel prop or are changing to one the blade geometry of the prop can make a lot of difference in speed and RPM.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor
8. Manufacturer?s recommended WOT range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Does it have a hydrafoil or trim tabs
11. Make, model, diameter, pitch and whether SS or aluminum prop
11. WOT RPM and speed from prop, how much gas and how many people in boat for test data
The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.

H

 

[redbull1]

Re: volvo prop

hwsii i have some more information for you regarding my boat and prop

1.1995 lund 1800 fisherman adventurer series
2.18' long 86" wide boat weighs roughly 2350 lbs.
3. 3-4 people
4. fishing
5. 15 degree deadrise
6. motor is a complete rebuild 3.0 4 cylinder GS
7.135 hp 1.87 gearing in a volvo sx outdrive
8.4400-4800 rpm
9.the boat has an sst hydrofoil
10.i could only get 26 mph@3500 rpm with one person in the boat with a 4-blade 16 pitch 14" diameter.
Thanks for any info you can provide

 

[hwsiii]

Re: volvo prop

Do me a favor, take off the hydrofoil and rerun the boat with both the 16" and the 21" and give me the WOT RPM and speed for each one, something doesn't appear to be right here, also how high is the antiventilation plate above the bottom of the boat measure it with a straight edge on the bottom coming out to the AV plate. I also need to know the make and model of each prop as well. After that I can make a recommendation.

H

 

[MikDee]

Re: volvo prop

also how high is the antiventilation plate above the bottom of the boat measure it with a straight edge on the bottom coming out to the AV plate.

It's an I/O hwsiii, this is not adjustable

redbull, Somethings not right, That boat should do 40mph easy, with that light a load.

 

[hwsiii]

Re: volvo prop

LOL I forgot Mik, too many things going on at once. But i bet when he pulls the hydrofoil off we will see a good change.

H

 

[redbull1]

Re: volvo prop

do you think the hydrofoil would make that big of differance and if so what is the reason?

 

[hwsiii]

Re: volvo prop

Because of the drag that it produces, especially when it is deep in the water with an inboard outboard. I expect a 2 to 5 MPH difference in speed.

H

 

[redbull1]

Re: volvo prop

Went to the lake... removed hydrofoil didn't notice too much of a difference (except for porpoising). Put 15x15 pirahana prop, didn't notice much until we removed spark arrester. We then noticed 600 rpm gain at 4000 rpm but did not gain any top speed with 3 guys. Went by myself and hit 4600 rpm's, once again no mph gain. Tried 15x17 pirahana, lost 200 rpm's from the 15 and recieved the same mph. Then tried 14x19 pirhana and lost 1000 rpm's...any input would be greatly appreciated. Thank you.

 

[hwsiii]

Re: volvo prop

Where are the speed and RPM numbers.

H

 

[redbull1]

Re: volvo prop

speed with the 15x15 was25 mph at 4400rpm

 

[hwsiii]

Re: volvo prop

You ran 3 different props and have given me only 1 number, there is no way I can do a comparison. I will tell you the 15" prop had a 25% prop slip.

H

 

[redbull1]

Re: volvo prop

the 15x17 was at 4000 rpm and 26 mph
the 15x15 was 4400 rpm and 25 mph
the 14x19 was 3500 rpm and right around 20 mph

 

[hwsiii]

Re: volvo prop

Redbull, if the gear ratio and the numbers you gave me for RPM and speed are right, then your motor is producing less than half of the 135 HP that it is supposed to produce. You have a problem, I have to assume it is the motor or something connected to it, it is not the props. You are showing very high prop slip except for the 16" 4 blade which is at 8%, but it is acting like the 19" pitch piranha with the same RPM but with a much lower prop slip. You should be running an 18" pitch prop, but yet you can't even get a 15" piranha to full RPM.
When you said you took off the spark arrestor did you mean off the alternator or the carburetor flame arrestor. I assumed you meant the flame arrestor because the RPM picked up dramatically and I think that was because of the extra air that was available to the engine because of the clogged filter.
I not only used my formulas for this analysis but I also ran the numbers through Crouch's formulas and Savitsky's as well, and they all agree with mine, so I am certain of my analysis.
You need to check everything from compression to throttle linkage and makiing sure the butterfly is opening all the way to the vertical position when you have the throttle pushed wide open.

Here are my numbers.

Boat and Motor

Prop Picker

Prop Slip

H

 

[redbull1]

Re: volvo prop

I checked butterflies on carb and they are opening up all the way, waiting for shunt so i can check timing myself and make sure advance is working properly and will go out later this week with gps and will also check tach.Thanks for all youre help so far hwsiii. Will post what i find out after we head out to the lake.

 

[hwsiii]

Re: volvo prop

That sounds great, I will be waiting.


H