prop question , What to do ?

[JJB]

I have a 20' bayliner with a 175 Johnson on it . The motor is raised to where cave plate is 1" above bottom of V and at max mounting height on boat . I had a 18" 4 blade apollo ss prop to start with and got around 5200 max wot . I then put a solas aluminum 3 blade 17" prop and my rpm drop to 5100 max wot . Some have suggest to use a jack plate to raise engine height which I am considering doing but need to know if my hydraulic steering will work with it . I have been told there is a small hook in the hull , would this effect the max rpm I am able to reach with this boat and motor ? Thanks for all your input on this one ! .

 

[steelespike]

Re: prop question , What to do ?

I'm not experienced enough to tell you exactly why your rpm dropped other than simply saying prop design.Typically a stainless will give more efficient
thrust possibly lowering rpm compared to similar aluminum.but 4 blades also usually reduce max rpm.compared to a similar 3 blade.
We really need the max rpm and speed for both props to tell where you are at.A hook could make the boat lay down too much causing extra drag.It depends on how much hook.The hook would make it difficult for boat to reach its ideal speed.Rpm could be met by prop selection.Does the boat seem to plow or be difficult to get the bow up.
It does appear you need to get your rpm up some more probably at least 5,500.A jack plate will allow better adjustment and usually gets the prop into cleaner water.Iwouldn't worry about weight.

 

[JJB]

Re: prop question , What to do ?

Thanks steelesspike , the max rpm for the 18" ss 4 blade was 5200 at 45 mph and the 17" 3 blade aluminum was 5100 at 42 mph . The boat planes off well but when trimed up the bow won't lift much and wont effect the rpm much either . Do most jack plates work with hydraulic steering ?

 

[MikDee]

Re: prop question , What to do ?

A hook in the hull would definitly bring the bow down on plane. Have you tried trimming up with the 17 at WOT? IMO, it seems like you lost some bow lift (extra bow lift usually provided by the 4 blade), and now you're boat is riding a bit deeper in the bow when on plane, slowing it down, & robbing rpm. I don't know if raising your engine any is gonna help this, anymore the just power trimming out as fasr as you can on plane.

 

[JJB]

Re: prop question , What to do ?

Mikdee ,do you think a four blade 17" ss would be better then the 17" 3 blade aluminum ? and who makes the better 4 blade ss prop that might help this type of problem ?

 

[ddaigle]

Re: prop question , What to do ?

If you cant get the front up the setback provided by a jackplate will help move your center of gravity back and make it much easier to get the front up and will increase your speed and rpm.

 

[JJB]

Re: prop question , What to do ?

If I did go with a jack plate my concern is with my hydraulic sea star steering . Does anyone have exp with extending the steering cyl to accommodate for jack plate so it dont hit the transom when tilted up ?

 

[MikDee]

Re: prop question , What to do ?

Mikdee ,do you think a four blade 17" ss would be better then the 17" 3 blade aluminum ? and who makes the better 4 blade ss prop that might help this type of problem ?

Apparently on your boat, there is either a hook in the bottom, or it's bow heavy? (can you change the latter?) It would be better, If you could get the bow up,,, usually a switch to less pitch, one less blade on the prop, and going from SS to aluminum combined, would raise your rpm 500, But in your case the 4-blade works better. I need to know what rpm you are looking to acheive? to recommend a prop,,, a 4-blade 17 pitch may only get you 200rpm especially being SS, you might be better off with a 16" pitch 4-blade, which should give you 400-500rpm more, I like the Apollo, I think it's a good prop.

 

[walleyehed]

Re: prop question , What to do ?

Most 4-blds that will work in this class of rig will "climb" to the surface...stern-lift....you need bow-lift, such as a Raker, Turbo1, Turbo Lightning. The same reason we don't like to run 4-blds on Bassboats with no natural bow-lift, such as a Ranger.
If the hull is hooked, that's hard to get around....period. It becomes a fine balancing act that "usually" a jackplate will help with (4"-6") no more than that...and a good bow-lifting 3-bld such as a first or second generation Raker..Look for a 3/8" vent hole.
What year is this engine?...need to know if it's the crossflow or a looper....top RPM will be different.

 

[JJB]

Re: prop question , What to do ?

_________Thanks for your help walleyehed ! It's a 2000 175 Johnson . 5000 - 5500 wot range . Its on a 20' bayliner cuddy wa deep v hull . 2 people , 40 gal of fuel with about 300lb of added weight lots of offshore running . SO the jack plate is the way to go with this and a Raker 3 blade prop ! I have a 18" 4 blade apollo ss now and getting 5200 wot and about 45 mph with no added weight , that 4 blade sure works nice in choppy seas to bad its the wrong prop for the boat . what pitch would you suggest in a three blade ss by turbo ? what is a 3/8 vent hole ? Do you know of a Jack plate that works well with hydralic sea star systems ?

 

[walleyehed]

Re: prop question , What to do ?

I'd be looking at a Bob's Machine plate for starters.
I've seen a few situations where a prop such as a Raker, Lightning or T1 would lift the boat enough you'd thought the anchor was still out with the other props.
You could possibly have a situation where the jackplate might make that 4-bld come to life....It's obvious it's lifting more or you wouldn't have more RPM and speed with another 1" pitch and another blade.
The 4-bld is going to work best in rough seas and that "may" be the best choice....let me see if I can get Dhadley on this one....

 

[JJB]

Re: prop question , What to do ?

Thanks walleyehen for the help ! I check out jack plates on Bob's today

 

[Dhadley]

Re: prop question , What to do ?

Most boats have a hook. It helps them get on plane. Most boats that are generally packaged with "smaller" motors have more hook so they'll get up easy with less hp. It's not good or bad, it's just in the design for the intended use.

As for the steering, you'll be fine. Most boats with hydraulic plates have hydraulic steering. In rare cases you might hit the steering cylinder when tilting all the way, you just have to watch and be careful. It sounds like you'll be OK since you'll probably mount the motor fairly high on the plate. That should give you all the clearance you need.

To be honest, I don't see anything unusual about your prop situation. A 4 blade ss prop would be expected to run at a higher X dimension than a 3 blade aluminum prop (of basically the same designs). A 4 blade should run higher and a ss prop will be more efficient than an aluminum prop.

 

[JJB]

Re: prop question , What to do ?

Thanks Dhadley for you help on this and will let you know how I make out after I get a Jack plate on it . I was looking at the new 4-1 manual raise plate at Bobs 4-5 " set back and is under 20lbs . Good choice ?

 

[walleyehed]

Re: prop question , What to do ?

the 4-1 is what I have my 200 hanging on...I "think" Dhadley has 1 or 2 as well...he may have went to hydr., not sure...
I really like the 4-1..lots of options for set-up.

 

[JJB]

Re: prop question , What to do ?

Hey walleyehed Thank's for all the help on this after I get the jack plate on I will let you know how it works with the 18 4 blade ss I have and go from there !

 

[walleyehed]

Re: prop question , What to do ?

Yes, please keep us posted...that's how we all learn, and if some adjusting is needed, maybe we can help you through that as well...Good luck!

Also, thanks Dhadley for commenting on the hook and expected results of the 4 vs. 3....thanks, Sir!

 

[JJB]

Re: prop question , What to do ?

yes ,I like to second that thanks to Dahadley about the hook ! feel a lot better about that one . My boat always felt under power with the 150 force . Thanks again to the I boat form it a great place for advice and better then most shops . Will keep you posted ! JJB

 

[Dhadley]

Re: prop question , What to do ?

I've run several of the 4 in 1's, like them a lot. I have a Bob's hydraulic on the Hewes now. Obviously we do a lot of shallow stuff with a flats boat so the button comes in handy. I think the 4 in 1 will be very sufficient for your use. Good luck, keep us posted!

 

[JJB]

Re: prop question , What to do ?

Hey walleyehed ,and Dhadley ,Thanks agaion for the advise on the jack plate . The boat rides so much better with it . Planes nicer and bow has a nice lift at a nice ridding speed . a few pictures of it below