Prop Help 27 Ultra Shadow MCOB
 

Just put in a merc 525 Whipple (775hp?) it came with a IMCO SC -1 shortie 1.36 gears 2 inch spacer. this boat come with a high x demension, so the 2 inch spacer is a must (I think). also came with a P5X 25 pitch. First Test drive it seemed to take a little more rpm's to get it on plane. and at about 5200 rpm i was running about 83-84, with more room to go. i'm not as worried about top speed as i am about cruzing speed to pull the kids on tubes. if i get to 90 i'm happy, and i don't want to hit the rev limiter.

any help would be appreciated!:lolhit:

Where is your rev limiter set at?
We do need to know if you can hit the limiter.
We can always go down in pitch and up in diameter to improve acceleration and maintain cruise or up in pitch to increase cruise.
There are options once we know more about the boats personality. It would make sense to give me a call at you convenience.

Brett

Brett

Will do Brett...hope to take it out for our annual New Years Day Lake Run and will take some readings then.

Hi Brett,

Took the boat out today. Had 6 people and about 35 gallons of fuel on one side and 7 on the other. Not ideal conditions,I know. First run everyone was sitting in the back and couldn't get it on plane. Moved 4 to the bow and around 4000 rpm, some s turns it got on plane with the tabs down. Limiter is 6000 rpm sand hit that easily. So I'm concerned that I can't get on plane yet I don't have enough prop for wot.

Thoughts?

Sounds like the prop is blowing out with the high X dimension. Is there a whale tail on the drive? Should cure your problem.
I would also recommend contacting John West (the guy who built the boat) or Shippingguy on Riverdavesplace.com. Either one of
those guys know that boat very well.

4czn10

Ok, so we know the propeller is too small and potentially the X dimension is too high.
A whale tail is a band aid for some applications but not appropriate for this type of performance application.
I would suggest starting with a test of a 28 Maximus propeller. We have these for testing at Bblades for a $55 fee.
Then, depending on results, we may want to test a 3" spacer. We have those for testing as well.
We are going to need a top speed and rpm to determine your slip % too. If you know what the speed was at 5900 or 6000 we can check the current %.

Let me know if we can help.

Brett

Thanks Brett. What about a drive plate? (Kind of like whale tail, but smaller and made of stainless) Riverdavesplace said he makes them...but I haven't heard back from him yet. I'm going to have to make another pass to get mph. Remember I'm running a 1.36 gears.

I'm not familiar with the drive plate product.
What I can tell you is planning without additional drive additions is the best option. Added units can create drag and deter speed and boat attitude. Best case is correct X dimension and propeller selection as well as CG adjustments and you will reap the best performance results.

Brett

Brett

Thanks Brett. i'm not looking to be the fastest Ultra out there . if i'm in the low to mid 90's i'm happy. i want to be able to plane easier, and be able to cruise efficiently, maybe pull the kids inner-tubing. when you mean correct the x dimension, do you mean go to a 3" spacer? how do you adjust CG?

As soon as i get the engine stall worked out, i can work with you on next steps.

Thanks.

Sounds good. Let us know when the engine issues and the testing there after is completed and we'll do what ever we can to help you get to your goal.

Brett