Prop/ trim Question

[metalwizard]

Last year I added smart tabs to my boat. and only had one quickie chance to take it out.. they worked pretty good.

Got her out yesterday (NICE) and had some time to try some stuff out.

Ok heres what it is 73 arrowglass viper tri hull 17.5 foot
165 HP I/O omc 800 (I believe) stringer..


Got it on the water and it get on plane withOUT porpoising AND FAST!!

My speedo is wrong but it gives me a reading so I ma using that for a basepoint.

Before the smart tabs I could get it to 4000 RPM WOT.. and made about 29 to 30 on the speedo (felt WAY faster)
with the tabs this year.. 4500 WOT at 35-37 MPH on the speedo (feels like what 40+ feels like on my partners boat)

So I know the RPM should be closer to 4000 SO I am thinking prop change.. I BELIEVE my prop is a 14/15 (14" diam)
Whatever it is do I want to go BIGGER pitch (make the 15 a 16) to bring the R's down and maybe the top speed up??

Remember I could Be wrong on that number... what I really wnat to know do I go UP a pitch number or Down.. Up seems Right to me..

Thanks..

 

[metalwizard]

Re: Prop/ trim Question

One more Question.. it turns REALLY easy to the left.. but kind of hard to the right... If I let go of the helm... it goes whatever way I leave it pointed (so if I m going straight it stays straight) Could that be the trim??? I rebuilt the drive last year and made one out of Two drives so I KNOW that may not be set right..

thanks

 

[JSMoore]

Re: Prop/ trim Question

Hey Wizard,
On the prop, increase the pitch to 16 or 17. In theory, each inch of increase will change the RPM by a 200 +/- RPM.

Steering effort should be roughly the same in both directions. I'm not familiar with the Stringers. But, my Cobra has a trim tab in back of the prop, on the bottom of the cavitation plate that will adjust the steering.
Cheers!
JSMoore

 

[metalwizard]

Re: Prop/ trim Question

Thanks For the reply JS.. That is what I thought.. thanks for the numbers too ,the 200 RPM is a good thing to know props aint cheap LOL

I do have a tab in on the back I guess just try changing that ans see what happens!

Oh and thanks to the mod for moving the thread.. I thought about it after I posted it.. I'm in the wrong spot.. Oh well, not any more..

 

[JSMoore]

Re: Prop/ trim Question

I do have a tab in on the back I guess just try changing that ans see what happens!

If you adjust the tab, do it a TINY bit at a time. A very small change in the tab can make a huge difference in steering.
Cheers!
JSMoore

 

[Texasmark]

Re: Prop/ trim Question

If you have "no feedback steering", adjusting the tab may help you.....turn the rear of it in the direction the boat steers hardest which for you would be to the starboard (right). This will put reverse pressure on the engine and help it to move in the opposite direction.

If you don't have no feedback steering and you can do as you said, remove your hands from the wheel at your preferred operating point and the boat remains at the previous heading, then maybe not. Sometimes the prop type will influence that difference in steering L to R. I have read on here where people have changed prop types/pitch and have affected steering.

If you have trim, the trim position can change the effect of the tab. You can set it up for where you usually run and drastically change your trim and drastically change your steering....nature of the beast.

HTH,
Mark

 

[metalwizard]

Re: Prop/ trim Question

Admiral. Some of that went over my head..

No Feedback steering?? not sure what that means. I can tell you this, its OMC tru course (cable steered) and the cable was supposedly changed shortly before I bought it last year (it looks really new)

I do have trim (I assume you mean motor tilt/trim) I put a new motor on for that and the trim works perfect. runs all the way up and down. But honestly since I put the smart tabs on it does not seem to make a whole lot of differance no matter where I run the trim.. so I have it pretty close to center..

The prop is stock, and to get my R's down a little (I believe 4000 is where I should be) I am probably going to go to a high pitch. once I get that on I will try to adjust the "tab" the
opposite direction" adjustment makes total sense.. if I push the drive to the starboard, then it will steer to the starboard easier.. because I am putting pressure that direction..

thanks for the input Both of you!!

 

[Texasmark]

Re: Prop/ trim Question

Admiral. Some of that went over my head..

No Feedback steering?? not sure what that means. I can tell you this, its OMC tru course (cable steered) and the cable was supposedly changed shortly before I bought it last year (it looks really new)

I do have trim (I assume you mean motor tilt/trim) I put a new motor on for that and the trim works perfect. runs all the way up and down. But honestly since I put the smart tabs on it does not seem to make a whole lot of differance no matter where I run the trim.. so I have it pretty close to center..

The prop is stock, and to get my R's down a little (I believe 4000 is where I should be) I am probably going to go to a high pitch. once I get that on I will try to adjust the "tab" the
opposite direction" adjustment makes total sense.. if I push the drive to the starboard, then it will steer to the starboard easier.. because I am putting pressure that direction..

thanks for the input Both of you!!

No Feedback Steering is a "trademark" for a type of single cable steering manufactured by Teleflex/Morse. I haven't dug into the hows, but the whys are that in most instances, you can release the steering wheel (take your hands off it), regardless of what the engine is doing and the wheel remains where you left it. This is good and a real safety measure.

I can understand the tabs nullifying your trim, especially in the outer positions; trim tucked in they should have less effect as they are coming up in the air (so to speak). On your engine trim being trimmed out (power trim and tilt pushing the lower unit away from the transom) trying to tilt the bow (nose) of the boat up and out of the water which changes the angle between the transom and water, pushing the rear of the angle (if you will) farther into the water, but the tabs are there to prevent that so you get a net zero effect on your trim out setting. Sounds normal to me.

Mark

 

[metalwizard]

Re: Prop/ trim Question

Thanks TEX that makes total sense..

I dont think my steering is "No Feedback" it is OMC True course.. but they sound pretty similar is theory!!

thanks for the input.... cant wait for the weekend!!

 

[metalwizard]

Re: Prop/ trim Question

Well I set the steering tab in the back to center (IT WAS WAY to one side) took it out today. steers MUCH better. still might need a tiny bit of adjustment but not much.

I also had 2 adults and 4 kids with me. boat rode much deeper in the water. fastest i got in the speedo was 32 MPH still at about 4200-4300 rpm.. (again I am not sure the speedo is accurate) towed the kids on the tube. without getting to WOT it towed them nice at 25 to maybe 30 mph.. could have got a little more but there were a LOT of boats out and the water was a little choppy

I may stick with this prop, although I did beat it up some more.. How the heck??? I never hit bottom that I was aware of.. Wish I could find a SS prop instead of this old *** aluminum one..