Tabs or Prop First?

[MRS]

OK Boat runs wot 3600rpm's I know this is low (86 4.3 omc 19' Candia) motor and outdrive in great shape. Will the smart tabs make a difference in the rpm's or should I change prop first to get the rpm's up first, prop now is 14 1/2 X 21 mph 44 was thinking of going to 14 1/2 X 19 on the prop. Tabs will be the stainless smart tabs with the pro trollers. Thanks for any reply's.....

 

[trendsetter240]

Re: Tabs or Prop First?

OK Boat runs wot 3600rpm's I know this is low (86 4.3 omc 19' Candia) motor and outdrive in great shape. Will the smart tabs make a difference in the rpm's or should I change prop first to get the rpm's up first, prop now is 14 1/2 X 21 mph 44 was thinking of going to 14 1/2 X 19 on the prop. Tabs will be the stainless smart tabs with the pro trollers. Thanks for any reply's.....

Hey there, you're right that your WOT rpms are low; I'm not sure of the correct range for that motor but you need to prop for the high end of the manufacturers recommended range.

Going to a 19" pitch prop may not get you to the right rpm. You may need to go as low as a 17".


Read this post by hwsii, it's very informative on determining the RPM change based upon prop pitch.

http://forums.iboats.com/showthread.php?t=365653

 

[MRS]

Re: Tabs or Prop First?

trend, thanks with the link you put in I think the 19 will add just about what I need for wot looks like it will add another 600rpm's (4200/4800) I did not know if the tabs would help raise the rpm's or not. I have never run tabs before but I am defenitly going to run them on this boat. Thanks again for the reply.

 

[nlain]

Re: Tabs or Prop First?

From someone running the stainless Smart Tabs, they do everything advertised. Once you get the wot rpms in the right range then add the tabs and adjust them and you will know the difference immediately, on plane much quicker with much less bow rise, same rpm cruise will give more mph, wot could increase 2 to 4 mph, use less fuel, low speed wander will go away, will handle rough water much better, as I said they do everything advertised. You will like them, I know I like mine.

 

[MRS]

Re: Tabs or Prop First?

nlain, I checked out your installation you did on your boat nice! I do get horrable bow rise even with drive all the way down even worse when pulling tubes. I will get prop dialed in first and then add tabs top speed is fast enough now for me. But if runs smoother with the tabs a few more mph will probably feel nice Thanks.....

 

[nlain]

Re: Tabs or Prop First?

You are welcome, you will probably that you can get on plane easier at a little over half throttle after tabs than you did at full throttle before tabs. I usually roll throttle to about 3500 rpm and get on plane and back off to maintain 3500 for cruise. Before tabs I had to be careful around 18 to 20 mph or I would start to drop off plane, I have got as low as about 14 to 15 without dropping off, makes running the rough water in the sound better, trim down a little, slow and on plane.

 

[QC]

Re: Tabs or Prop First?

Hey MRS

Yeah, prop first, but we need to confirm your tach. RPM low, plus decent top speed (44) makes me wonder always, and I never trust tachs without confirming. Do you know your gear ratio? I find a 1.68. If so the tach is off as I am getting a negative slip number which is basically impossible . . . I'm getting around 4200 RPM with a very good slip of around 12%.

Speed is GPS?

 

[slasmith1]

Re: Tabs or Prop First?

I will probably take some flak for this but..... on a 19' or larger boat you may want to consider the extra money for adjustable tabs such as bennett. this is especially true if you boat anywhere with strong currents where you might encounter following sea conditions.

 

[MRS]

Re: Tabs or Prop First?

Hey QC, hope you had a great Christmas it is 1.68 and seems to match the tach. from 3000rpms=30mph 31mph=31mph up to 3600rpms. then the motor does sound the same but boat picks up speed only hit 44mph once at cottonwood but had to slow down when hit the narrows headed back to Katherins landing was really smooth at cottonwood and you know how it changes on the way to Katherins. How would I verify that the tach. is reading true? I really do love this boat and if you remember my old boat 17ft. 120 merc. it would almost hit 30mph. if everything was just right. We gave it to the kids and they just love it is there first boat Thanks for any help.....

 

[MRS]

Re: Tabs or Prop First?

I will probably take some flak for this but..... on a 19' or larger boat you may want to consider the extra money for adjustable tabs such as bennett. this is especially true if you boat anywhere with strong currents where you might encounter following sea conditions.

slasmith, no flak here I 99% of the time in fresh water pulling tubes and fishing mostly fishing. I like the idea of self ajusting so if I am pulling the kids can consentrate on them and not worry about ajusting to much stuff. Thanks for your input.....

 

[QC]

Re: Tabs or Prop First?

Merry Xmas to you too dude.. Say hey to Mrs MRS too K?

On the tach, the RPM match speed thing seems like normal slip (15%), so the tach sounds closer now with the exception of the 44 MPH . . . How'd you get that speed number?

I will probably take some flak for this but..... on a 19' or larger boat you may want to consider the extra money for adjustable tabs such as bennett.

You won't get any flak from me. I feel 100% the same with the only two issues being budget and whether or not you are the type that likes to play with stuff (tab switches) or a point it and go guy . . . point it and go = smart tabs, budget is budget.

 

[MRS]

Re: Tabs or Prop First?

QC, did get 40mph with gps and speedo read 42-43mph did not get 44mph with gps but speedo read 46mph. I will have to try again with gps, but 40 is great if that is what I can only get. I still have boat off trailer redoing bunk boards and painting trailer just to cold today to paint. As soon as I can finish trailer we are headed back to Havasu and will give a gps run with 21 and 19 props Thanks.....

 

[MRS]

Re: UPDATE Tabs or Prop First?

Re: UPDATE Tabs or Prop First?

OK, 19p turning point prop on the way trailer done should be in the water soon........

 

[MRS]

Re: UPDATE Tabs or Prop First?

Re: UPDATE Tabs or Prop First?

OK, 19p turning point prop on the way trailer done should be in the water soon........

Did get my 19p prop from iboats now waiting to get it in the water. But the water might come to me. Rained all week here roads are all flooded or closed so hopefully get to test it next week I hope.

 

[QC]

Re: UPDATE Tabs or Prop First?

Re: UPDATE Tabs or Prop First?

Still raining here . . .

 

[MRS]

Re:UP DATE. Tabs or Prop First?

Re:UP DATE. Tabs or Prop First?

OK heading out tomorrow morning got 19p turning point prop tuned up motor changed oil cleaned boat will get gps speed.

 

[JimS123]

Re: Tabs or Prop First?

From someone running the stainless Smart Tabs, they do everything advertised. Once you get the wot rpms in the right range then add the tabs and adjust them and you will know the difference immediately, on plane much quicker with much less bow rise, same rpm cruise will give more mph, wot could increase 2 to 4 mph, use less fuel, low speed wander will go away, will handle rough water much better, as I said they do everything advertised. You will like them, I know I like mine.

That all makes sense, but if your prop is the same and your motor is turning the same rpm, how can the speed be faster?

 

[nlain]

Re: Tabs or Prop First?

That all makes sense, but if your prop is the same and your motor is turning the same rpm, how can the speed be faster?

I would say less boat in water, so less drag, I do know that my cruise speed increased at the same rpm, less fuel used on the standard trip that I make. I make the same run with about the same load and after the tabs were installed and adjusted I actually gained 3 to 4 mph at the same 3500 rpm. When running and I look over the side of the boat the water spray is coming out behind me where it used to come out about where my seat is. They do work and do everything advertised for me.

 

[MRS]

Re: Tabs or Prop First?

OK, went out today had a 21p prop before ran 3600 rpms ran a 19p prop and still ran 3600 rpm's both run 40mph on gps. Motor runs and idles good but feels like it wants to run better I am going to check timing could that be it? I also changed plugs wires rotor and dist-cap did not change points they did look good and were gapped right I do have a new set of points and condensor will go ahead and replace. Am I on the right track?
All considered the day was excellent weather and glad to be on the water. Thanks for any replys......

 

[JimS123]

Re: Tabs or Prop First?

I would say less boat in water, so less drag, I do know that my cruise speed increased at the same rpm, less fuel used on the standard trip that I make. I make the same run with about the same load and after the tabs were installed and adjusted I actually gained 3 to 4 mph at the same 3500 rpm. When running and I look over the side of the boat the water spray is coming out behind me where it used to come out about where my seat is. They do work and do everything advertised for me.

RPM, weight, weather, wind, prop, etc. Obviously, one very important parameter has been left out of the equation....Engine trim. When I performance test, my data sheet has a slot to record my trim gage reading. I chart RPM vs. MPH vs. GPH at several settings.

If the water is breaking farther aft, then the motor is trimmed out further, thus that accounts for the increase in speed. So maybe the tabs "allowed" more positive trim.