Merc 4.3 prop advice

[yaw]

Hey all,

Looking for some prop advice. See below.

1) Performance issue you are trying to correct. - Maximum hole shot, and better low speed maneuvering. I'm getting lots of bow wonder at low speeds.

2) Current prop manufacturer, model, aluminum or stainless as a minimum. - Merc tempest plus with the large vent plugs. It's SS.

3) Current prop diameter and pitch (required). - 14 5/8, 21p

4) Wide open throttle RPM and speed with an average load (very helpful) - 4600 rpm and 48mph (gps). That was me, 3 small kids, and a full tank a fuel.

5) Engine/drive make, model, year, and HP - 2014 merc 4.3 TKS 190HP. Alpha one drive with 1.81 ratio.

6) Boat make model, year, length and weight - 2014 Bayliner 185. I don't recall the weight, but I think it's around 2500lbs.

Thanks!

 

[Maclin]

Welcome aboard!

You are getting very good numbers with the current 21p Tempest prop. Well below 10% on slip factor, closer to 5-6. Conventional wisdom will say to go to a 19p in same prop/brand/model for better holeshot, sacrificing top MPH to 45 at slightly higher 4800 rpm's estimated, using 6% slip. Your full goose bozo obtainable RPMs' at WOT may then probably be in over-rev territory.

For towing holeshot going to a 4blade or similar would help there, but being different styles of props the pitch might be a dice roll.

Regarding the low speed maneuvering, depending on how low of speed you are talking about, under 10 or around headway speed you may be experiencing the I/O wander. Besides just getting used to it and not over correcting, the only thing that can help that is a dual prop drive.

Bow steer is also probable, you can get that when trimmed all the way down at planing speeds, and the bow catches more of what the water wants to do with you instead of you cutting though it at a higher trim level.

Your boat sounds like a lot of fun!

 

[yaw]

Thanks for the reply! Yes, the boat is a blast! We are really enjoying it.

The low speed maneuvering is very low speed. Definitely under 10mph. I notice it most when approaching the dock. I think you're definitely right about not over correcting. I noticed that small adjustments in steering definitely helped.

Should I make any adjustments to the ventilation holes on the prop? I see they make different sizes, but I'm
Not sure if I need to make a change. The engine revs to around 3200 rpm during the hole shot, and stays there until I get on plane and start trimming out.

Thanks again!

 

[Maclin]

Do you have the tuning vent holes plugged now? Hopefully you will get some more responses soon. I have no experience in the vent hole tuning. Good luck!

 

[Maclin]

I guess I do have some experiene with those, if the water is rough then when you run a prop with vent holes open the prop will have a propensity to cavitate early and often as the stern experiences the wave action.

 

[Maclin]

Ok, your first task is to get one more post in so you can post pics. Then POST PICS lol . Here We luvs us some pics.

 

[QBhoy]

Very good numbers, I'd say !
I'm afraid steering wander at slow speeds is an inherent problem with most planing hulls. The shorter they are, the worse it is.
I would keep it as is with the prop....you seem to be dialled right in and she would most likely easily make max rpm of 4800 with less fuel and less family. Haha.

 

[yaw]

Do you have the tuning vent holes plugged now? Hopefully you will get some more responses soon. I have no experience in the vent hole tuning. Good luck!

I don't have them totally plugged. They have the large size plugs in them now.

 

[yaw]

Ok, your first task is to get one more post in so you can post pics. Then POST PICS lol . Here We luvs us some pics.

Haha. Well, I will see what I can do. I'll have to take some the next time I'm out.

 

[yaw]

Very good numbers, I'd say !
I'm afraid steering wander at slow speeds is an inherent problem with most planing hulls. The shorter they are, the worse it is.
I would keep it as is with the prop....you seem to be dialled right in and she would most likely easily make max rpm of 4800 with less fuel and less family. Haha.

Sounds good. Thanks for the advice!

 

[yaw]

No Title

Here's a pic!

 

[Maclin]

Likin' it so far, nice lines. Wake tower looks "organic"