Crownline 250 CR having trouble planing

[buoycall]

Quick summary
2006 Crownline 250 CR
350 Mag
Bravo 3, 22p
weight (6800 lbs)
75 gallon fuel (475 lbs)
25 gallon water (200 lbs)
6 adults (1000 lbs)
Misc (100 lbs)
total (8575 lbs)

I am having trouble planning on my boat even when trim tabs are fully downward. With the engine at full throttle, I can not exceed 3100-3200 rpm until it has planed. Once it has planed, it drives like normal (5100 rpm). The engine starts easy, idles smoothly, and at full throttle sounds typical. Also, I has the same experience trying to pull a child on a tube. Is this normal? Does Mercruiser have a rpm limited as a safety until a plan has been achieved? What could the problem be? Overweight? bad engine?

 

[blackhawk180]

Re: Crownline 250 CR having trouble planing

Welcome bouycall and thanks for providing all the info!
It looks like you are overweight but you didn't mention how it performs when you are solo? If it's still hard to get onto plane running light, then something else is the problem. I'm nearly positive there is no RPM limiter so the problem seems to be you are overloading the motor (too much pitch/weight) until the boat planes out. Even with trim tabs? That's another indicator since they (tabs) usually reduce time to plane quite a bit. Are all the adults behind the windshield or are they evenly displaced? Run the test light and let us know the results.

 

[buoycall]

Re: Crownline 250 CR having trouble planing

Thanks for responding blackhawk180.
Majority of the people are sitting behind the glass. When it is my wife and I, I would say that it runs normal. Say if I push it full throttle, the RPM does hold at 3100 until it plans but it plans very quickly, so i have never really noticed it. I will assume that I was overloaded.

 

[Bob's Garage]

Re: Crownline 250 CR having trouble planing

Are you trimming your outdrive in? This will bring your bow down, helping the engine get the boat out of the water, onto plane. Then trim the outdrive up (out) to achieve the best "attitude". Use the trim tabs to balance the boat from left to right for a level ride.

If the outdrive is up too much, it will push the stern down, causing the boat to plow and wallow, trying to push too much water out of the way so it can get "on top".

 

[Mischief Managed]

Re: Crownline 250 CR having trouble planing

You have a lot of boat for a 350 MAG, so it's going to take awhile to plane. Since you can get to 5100 at WOT, perhaps bigger tabs would be a good idea. You can also try to reverse the location of the "celery stick" in the rear trim ram cross bar. If it's forward, push it out and put it behind the cross bar. That will give you about 1/2" more down trim. That said, this may cause stability issues, so do this with caution.

One other thing to try is to trim up earlier, my 7.4MPI actually planes faster if I trim up before it's cleanly on-plane and uncork the exhaust tube to let the engine breathe.

 

[Jonnybbad]

Re: Crownline 250 CR having trouble planing

I would say your prop is quite aggressive. My 24ft cruiser with a 350 has a 15p.

 

[smokeonthewater]

Re: Crownline 250 CR having trouble planing

I would say your prop is quite aggressive. My 24ft cruiser with a 350 has a 15p.

getting 5100 rpm when heavily loaded his props (two of them) are certainly not too highly pitched. He has a bravo III

 

[LippCJ7]

Re: Crownline 250 CR having trouble planing

Just FYI I have 26's on my 248 I think you could do better with a bigger prop set, but if you have had this boat for awhile and have not had this problem I would certainly find your problem before you change props.

Of course I have more motor but HP wise we are pretty much the same, I have more torque but not by much.

 

[bekosh]

Re: Crownline 250 CR having trouble planing

I've had a couple of friends with Crownline CR's and they had similar issues. One problem(?) is that Crownline mounted the motors and drives very deep to get a low floor. Because it's mounted so low you are dragging alot of hardware through the water until you get up on plane. You can somewhat see what I mean in this photo. So there may not be a whole lot that can be done about it.


EDIT: You may want to disregard this post. My friends had older mid to late 90's Crownlines. I don't know if they mount the drives that low on the newer style.

 

[Jonnybbad]

Re: Crownline 250 CR having trouble planing

getting 5100 rpm when heavily loaded his props (two of them) are certainly not too highly pitched. He has a bravo III

Hmm... the duo prop drives run a steeper pitch? I guess I was not aware.

 

[smokeonthewater]

Re: Crownline 250 CR having trouble planing

not all drives have the same ratio... even on two boats with alphas one could have a 1.5:1 ratio and the next could have a 1.98:1

I actually had a 26' flybridge cruiser with a 165 hp inline 6 and a 17" pitch prop .... worked perfect with a 1.98:1 upper but would have needed a much lower pitch with a 1.5:1

 

[frantically relaxing]

Re: Crownline 250 CR having trouble planing

Our old '88 Sun Runner Ultra 252/5.7 Volvo DP had a hard time getting on plane at times. With 3 adults, 2 dogs and assorted gear on board at 7700' altitude, it never did get on plane with the original B4 props. At 6300' altitude with just the 2 of us it was a 30 second ride before planing. I got a set of B3 props and we never had another problem at 6300', was still slow to plane at 7700' but not terrible. A friend had an '89 Four Winns 240 Sundowner with a very good running 460 King Cobra that would just stand up with more than 2 people in the thing. I changed the 19" pitch prop for a 17" and it made little difference. RPM's were 4200, trim tabs full down and all it would do was stand up, churn water and plow unless someone went up front. I took the boat out by myself once and it was like driving a rocket. But add 3 more people and it was nearly a useless boat. Never did figure that out.

The OP's boat sounds similar-- one thing that helped our Sun Runner, was loading LOTS of beverages and canned goods WAAAYY up front...