Can't get my boat on plane.

[Alan Dykes]

Hey guys,

I have a 1994 Chris Craft 282 Crowne cruiser with twin 5.0L engines, Volvo SX outdrives with 1.60 ratio. Props I have are 4 blade alum. 15" dia x 16" pitch and 3 blade stainless 14.75" x 17" pitch. They both perform about the same. Engines turn up to about 3000 but will not push it over on plane. It will occasionally get on plane and the engines will only go to 3600 at WOT. We had the aluminum props repitched to 11.5 pitch, and it only made about 200 rpms difference.

Things I have checked: Bottom of boat is clean. Throttles open fully. Engine timing is right.

What should I try next?

Thanks,
Alan

 

[airdvr1227]

Re: Can't get my boat on plane.

Couple things come to mind...

Is this a new problem? Did it run good before?

Not sure what the Wide Open Throttle RPMs should be but I'm guessing they should be more in the 4,000 range. There's a sticky at the top of the page that refers to thinkgs to check if you can't get WOT rpms.

http://forums.iboats.com/showthread.php?t=295070

Fixed it

 

[QC]

Re: Can't get my boat on plane.

Welcome aboard Alan!!!

The sticky is in the I/O section, under Adults Only : http://forums.iboats.com/showthread.php?t=468285

This being the non-engine section, let's keep this thread to possible boat issues, although I will break that suggestion immediately with a prop question . . . Going from 165 to 11.5 pitch causes me two issues:

1) "repitching" which is not purely good or possible from a totally technical standpoint, is usually considered 1 - 2 inches max. Going from 16 down to 11.5 causes lots of alarms to go off for me.
2) IF it was good, 200 RPM makes no sense although her limited planing ability would keep the associated RPM jump down too.

Back to boat issues. Does she have trim tabs? If so, do you know how to use them? Also, drive trim, are you trimming down all the way? Have you tried alternate trim positions to see if there is any positive impact?

Load? Can you throw out everything except fuel, one life jacket and you? Test as empty as possible? With that said, twin 5.0s in a 28 footer should actually be reasonably fast. High 40s is in the cards with everything right.

 

[greenbush future]

Re: Can't get my boat on plane.

If the engines and outdrive and props are in good order, you may check for extra water either
entering or already in the boat. Many boats soak up water under the floor, where all the floatation is at. I had a smaller run-about that was about 6-700 lbs too heavy, and it all was in the floatation stuff under the floor. Once I fixed this, the boat was very, very fast.
The RPM's sound low, what are the specs on them?

 

[QC]

Re: Can't get my boat on plane.

Typically no flotation in anything over 20ft. . . . Yes water entrapment could be an issue, but not soaked foam.

 

[CaptOchs]

Re: Can't get my boat on plane.

I had the same issue with an outboard. As it turns out ethanol in the fuel absorbed water and it was sucking that junk in my engine. I ran engine and gave a short squirt of starter fluid (i know, i know) into the carb and the boat jumped on plane. Do you have a fuel filter/water sep on your rig?

 

[Alan Dykes]

Re: Can't get my boat on plane.

Thanks for all the info so far. When we first got the boat, it would get on plane, but it wasn't easy. I do have trim tabs and are using them as suggested on Bennett's website. I looked at the link you gave me and have checked most of those things. I called Chris Craft and they said the prop for the boat was a 14.5d x 19p with a 1.76 ratio outdrive. My outdrives are 1.60.

I think there may be a drag issue. But the primary problem may be props, maybe I should put this question in that section too. I'm with QC, this thing should really perform with 420 HP.

Alan

 

[QC]

Re: Can't get my boat on plane.

I think there may be a drag issue.

Help me with that. You mean stuff on the hull?

I'm with QC, this thing should really perform with 420 HP.

I'm going to qualify that some. I just saw some pictures and this boat is called a 31 footer by some and she has a full 10ft. beam, so let's just say she's big boned . . . Low 40s would be acceptable.

 

[Alan Dykes]

Re: Can't get my boat on plane.

Help me with that. You mean stuff on the hull?

Well, I have checked the hull and it is slick. But something has changed. It used to plane out. It didn't do real good though. Maybe there is a little algae or something and it is just enough to keep it from breaking over because it was so marginal to begin with.


I'm going to qualify that some. I just saw some pictures and this boat is called a 31 footer by some and she has a full 10ft. beam, so let's just say she's big boned . . . Low 40s would be acceptable.

It measures 30 feet long and 9' at the stern. It is a pretty good size boat. It would only do 25 knots at WOT (3600rpm) when it would plane out. I am thinking of buying some 15 x 13 props to try. The only ones I can find are Volvo and they will be $400. I don't mind paying that if that will fix it. I wish I could buy props from somewhere that I could exchange them if they didn't work. Does such a place exist?

 

[25thmustang]

Re: Can't get my boat on plane.

There are definately issues with the boat.

Number one, do the motors run well? No issues at idle? Will they rev without a load to 4000-4500. I would imagine your WOT RPM should be in the 4400-4600 range, or close to it.

Number two, 3600 RPM and 25 knots on plane sounds close for a cruise RPM and speed, but it should be a lot more at WOT. Assuming quadrajets, your not even into the secondarys completely at 3600 RPM.

Number three, it might be worth checking the boats weight. Someone mentioned boats over 20' mostly don't have flotation foam, but some do (mine does). It might be worth seeing if there is any and if it's soaked, although I wouldn't imagine so.

To me, it sounds more like a problem with the motors, than the props, or even boat weight.

 

[Alan Dykes]

Re: Can't get my boat on plane.

There are definately issues with the boat.

Number one, do the motors run well? No issues at idle? Will they rev without a load to 4000-4500. I would imagine your WOT RPM should be in the 4400-4600 range, or close to it.

Number two, 3600 RPM and 25 knots on plane sounds close for a cruise RPM and speed, but it should be a lot more at WOT. Assuming quadrajets, your not even into the secondarys completely at 3600 RPM.

Number three, it might be worth checking the boats weight. Someone mentioned boats over 20' mostly don't have flotation foam, but some do (mine does). It might be worth seeing if there is any and if it's soaked, although I wouldn't imagine so.

To me, it sounds more like a problem with the motors, than the props, or even boat weight.

Yeah, I am fine with the 25 knots, I would love to have that back now. The engines run good, and they run identical. The only common item between the two that I am aware of is the fuel tank and as much fuel as we have pumped through these things it should be all fresh by now.

WOT should be 4400-4800. I found some 15x15 3 blade props for $100 each. I am thinking of trying them. The way I understand it that will be the equivalent of dropping 2" of pitch from a 15x16 4 blade. Is that right?

 

[Greg Mrozinski]

Re: Can't get my boat on plane.

WOT should be 4400-4800. I found some 15x15 3 blade props for $100 each. I am thinking of trying them. The way I understand it that will be the equivalent of dropping 2" of pitch from a 15x16 4 blade. Is that right?

Yes roughly. It should gain you about 600 more rpms at WOT. However, you will loose a little speed at cruise rpms.

 

[Maclin]

Re: Can't get my boat on plane.

The 1.76 ratio would make a lot of difference also. Just dropping pitch on the prop is not quite the same as having the correct ratio drive and then adjusting pitch. Do you know how it ended up with the wrong ratio drive?

 

[cobra1476]

Re: Can't get my boat on plane.

If the boat was planning right before it should be the same now. Unless you have a loss of power of some weight was added.

I would check and double check everything before purchasing new props.

 

[Alan Dykes]

Re: Can't get my boat on plane.

I'm going to pull it out this weekend and see what I can find. Thanks for all the ideas.

Alan