Having trouble getting on plain, different prop time?

[Chet labrozzi]

Yesterday I had 9 adults, full tank of gas and portable water tank filled, the waves where about 2 to 3 footers with high head winds. The motor is a 5.7 liter merc with 250 hp on a Crownline 238 deck boat. We had a heck of a time getting up on plain and then when we did the waves where so rough we had to back off, do I need a different diameter prop or different pitch? When there is 2 to 4 adults and the water is clam it does fine?

 

[craze1cars]

Re: Having trouble getting on plain, different prop time?

You need to make a choice...

Do you want your boat appropriately propped for 2 to 4 adults on calm water?

Or do you want your boat appropriately propped for 9 adults and full water & fuel tanks with headwind and 2-3 foot waves?

There is a HUGE difference, and you will absolutely need two different props for these two very different applications. On light days you will probably run your existing prop (assuming it is correct). On heavy days you will need to change props...most certainly to one of a lower pitch.

How much lower? I dunno. If you share your WOT throttle full speed and RPM data with your usual load on calm water, we can give you a better idea of what you might want for a prop in each of these conditions.

 

[Chet labrozzi]

Re: Having trouble getting on plain, different prop time?

On the return trip with the 9 adults the water was calm, what wind there was was behind us and we had no problem getting up and motoring. The waves where 0 to 1 foot. The rpm was right around 4000 and the speed if the speedometer is correct was right around 36, that was pretty much top speed with a 5.7 liter 250 hp on a Crownline 238db..Does that help?

 

[steelespike]

Re: Having trouble getting on plain, different prop time?

Do you have trim tabs?I'm not crazy about tabs but they can be very effective in controlling boat attitude,especially when rough.Of course moving some weight forward can help.I think you can see that 4 people in a stern seat could make planing pretty tough.

 

[Chet labrozzi]

Re: Having trouble getting on plain, different prop time?

I don't have trim tabs, we had four in the front and 5 in the back...i hate the thought of changing prop's all the time but it was a pain and appeared to be undered powered with the wind and high waves. Do you think the tabs would help? How would you of had the trim on the motor positioned?

 

[craze1cars]

Re: Having trouble getting on plain, different prop time?

Not sure what year this boat is....what is the RPM operating range of the engine? Usually it's stamped on a sticker on the top of the motor somewhere. I'll speculate late 90's/early 00's...which means correct operating max recommended range is very likely 4,400 to 4,800, as that's typical for a 5.7 of that vintage...newer MPI models sometimes a bit faster, older pre-vortec models sometimes a bit slower.

So if you were only getting 4,000 rpms at absolute max top speed, then you are well below where this engine should be running, and therefor that tells me that you are most certainly over-propped for that application. So for prop shopping for that particular condition you'd want to drop at least 2" of pitch...maybe even 4" of pitch...from your current prop, depending on the actual operating range of your particular motor. Such a drop would help your holeshot/planing dramatically.

I would do that before trim tabs. I completely agree tabs can certainly help substantially....but first you need to be appropriately propped.

 

[Chet labrozzi]

Re: Having trouble getting on plain, different prop time?

It's a 1998 and there are some stickers on the top which I will look at the next trip down to the boat. Also on Friday I am going out again so if the weather is nice i'll get the actual rpm at full throttle and advise. Thanks for the help.

 

[Texasmark]

Re: Having trouble getting on plain, different prop time?

Just a little tag along comment here: I don't think your boat was underpowered or under propped considering your operating conditions. You had a big load aboard and a big force against you in your initial complaint. You solved the problem yourself by what you said about your return trip. I agree, prop for what you do the most, and when in more severe environments, expect less performance, or prop for that and expect sloppy performance and neck snapping hole shots when lightly loaded in calm water.

My 2c,

Mark

 

[Chet labrozzi]

Re: Having trouble getting on plain, different prop time?

Ok Mark, thanks...It's a new boat much bigger and heavier so I'm in the process of trying to figure it out. That was only the third time out with this boat. I am still going to check the max rpm's etc but apperciate the advice.

 

[Mi duckdown]

Re: Having trouble getting on plain, different prop time?

As captain of the boat. you can tell people to move and sit where you want, for a better ride.

 

[Texasmark]

Re: Having trouble getting on plain, different prop time?

As captain of the boat. you can tell people to move and sit where you want, for a better ride.

Different strokes for different folks....to paraphrase a comedian on tv one evening that I saw. Or to put it another way, it is a boy thing with me to have proper resources so that my guests can be comfortable and relax as they wish.....yes I have been the "move forward on hole shot" route, but I corrected it. My choice.

Mark

 

[americaneagler77]

Re: Having trouble getting on plain, different prop time?

move the people temporarily to the front to get on plane then have them return to seats. not all the people but it will plane much better with majority of the weight in the front......