Max rpm on 96 90hp Rude

[Fishing Rod]

Hi All,

Trying to figure out where I should be at WOT.

Princecraft 169 Pro with a 13" x 19" aluminum prop.

Currently 36 mph on the speedo at 4600 rpm

Pulls great, just wondering if I should get more top end and if 4600 rpm is optimum.

Thanks
Rod

[Mick]

I'm no expert but my 115 HP merc tops out at 5700 ....4600 sound very low to me

[bostonwhaler]

I was always under the impression that 5500-5700 was WOT rpm as well

[Fishing Rod]

I figured it was low too.

[lape0019]

Are you trimming up at all? 4600 rpms is definitely low.

I did a bit of research and it looks like 5500-6000 is the norm provided you have a V4. Regardless, your RPMs should be over 5000. You are bogging that motor down at 4600 rpms.

If this is a new boat to you, there are a few thing you can try. What hole is the motor mounted in? If it is in the first hole on the bracket at the top, your motor may be mounted too low. Try raising it to the second hole.

If it is in the second hole, Your prop is too much for that motor.dropping to a 17p should gain you 200-400 rpm.

If you are not trimming up, start with that. My 75 will hit around 4800 before I start trimming up. I can trim it up almost all of the way to 5800 before she will blow out. My max rpm is 5500 so I don't go any higher than that.

If you can provide more info regarding these items, we may be able to help you out a bit more.

[Fishing Rod]

4600 is trimmed up as far as I can go before it "blows out". I have lots of experience with higher end performance boats.

I've only had the boat for a year and I'm just now trying to sort things out. The thing is it is a Princecraft package for 1996, so I would think the motor would be set at the right height. I don't see any witness marks from where the motor has been moved down.

My guess is someone has switched out the prop. To get it up another 1,000 rpm I think I not only need a smaller pitch but diameter as well?

I went into a Princecraft dealership and the guy was a bit rude (pun intended) telling me they use mercs now so don't bother asking him any questions.

BTW Thanks for all your input

[lape0019]

If you have experience with higher HP boats, the info should be transferable. I run a 13.25 x 17 on my 75 so I doubt you would need to go to a smaller diameter prop. Do you by chance know the LU gear ratio?

And the manufacturer rarely sets up a boat 100% properly from the factory. My boat was setup in the first hole and was over up to the second by the previous owner to get more speed by reducing drag. This would also increase rpms as it would not have to push so hard.

If you drop to a 17, you will gain some rpms. You could to to a 15 and would get the 1000rpms you are looking for but I don't know how well it would run top end and considering you say it has a good hole shot, I don't see a reason to go down that far.

If you are still in the first hole on the motor mount, I will say you would probably get the results your are looking for by raising the motor 1 hole and going to a 17p and keeping the diameter about the same.

I think your motor is just too low right now but without seeing it, I cannot be certain.

[Fishing Rod]

Here is how the motor sits. It is laying on the transom, so it is as low as it can go. No holes, but it can be adjusted up about 3".
The skeg placement looks about right to me with the lower cavitation plat just a bit higher than the bottom of the boat.
There is a chance the tach is out too, but 35 mph seems soooo slow.
Sorry about the sideways pics.