WOT question

[pdxsearay]

Hey friends. Finally had a chance to open up the throttle on my boat today (meaning, took it out without my wife on board). WOT for my engine is defined as 4400-4800 rpms per Sea Ray. At full throttle we got to 4200 very easily and then with trim adjustments got into 4400-4600. Is that what WOT is? Just getting to the rpms irrespective of speed ? My gps showed 48mph and change for what it’s worth. I suspect on a calm lake I could get to 50.

We needed some help to get to 4800 rpm but the water was a little choppy. Calm water & more trim adjustment could sometimes do the trick depending on conditions. Once when we we had the wind at our back & going with the current (was on a river) & water was glassy I saw it sneak up to 5k rpms.

We probably ran it for 3-4 min straight at WOT a few different times and the boat seemed very happy.

Anyway. Anything else I need to know about WOT? I recently switched from a 3 blade to a 4 blade prop so it was good to see the boat get there.
Thanks

 

[b_arrington]

You basically have it. WOT is the RPMS you can achieve at max throttle. Factors like drive trim, trim tabs, weight, and how clean / smooth your bottom is all affect your WOT.

If the range is 4400-4800, 4600 is in the range and you're good. The 4 blade prop you have will improve the hole shot and lower the speed at which you can stay on plane vs. a 3 blade. But you give up a little top end speed and (I think) lower the max WOT RPMs. At 48 mph I think that's a pretty good speed though!

You should note down your RPMs an speed at WOT. This is a good benchmark reference in case you have any issues. If you can't get to the same RPM or speed at WOT you may have a issue. I noticed my speed was way down for my WOT until I had my clumpy bottom paint removed.

 

[pdxsearay]

Thanks- good to know.

yeah that's exactly why i got the 4 blade - quicker plane & stay there at lower speeds. I have smart tabs going in next week to help further with both of those things. Good call on jotting down the engine performance stats. I might swap in the 3 blade next time i go out and see if that has any effect on RPM or max speed.

48 mph is good, but i do have the 4.3L instead of the 3.0 so i was hoping we could a little faster. But it will be a rare occasion either way to be maxing out the speed. The willamette river which goes through portand is wide and deep but it has stronger currents and can get choppy.

 

[sbw1]

A little bit of chop actually helps your WOT and top speed as you do not get stuck in the glassy flat water. Your boat is running great.

 

[Stingrayaxe]

If top end is your goal then your 4 blade is holding you back. Depending on the pitch of your 3 blade you should see top end improvement. It sounds like hole shot and lower speed to plane is more of your goal. If so, the 4 blade is where you want to be. Trim tabs will help a lot. Let us know the changes in performance once the tabs are installed.

 

[Leardriver]

Wide open rpm's is measured my way by the standard load you will have with people and fuel. I want to hit the top number, because we pull slalom water skiers.

 

[pdxsearay]

A little bit of chop actually helps your WOT and top speed as you do not get stuck in the glassy flat water.

interesting. Is that because it requires more power and hence more RPM to get through the water?

It sounds like hole shot and lower speed to plane is more of your goal. If so, the 4 blade is where you want to be. Trim tabs will help a lot. Let us know the changes in performance once the tabs are installed.

For sure. I will report back on performance from the tabs. I went with Nauticus over Bennett for the self-leveling tabs because i preferred the gas actuator to spring and I liked that they had more customization options rather than one size fits all. Although i suspect at my boat's size and what my goals are it doesn't really matter between the two. we'll see.

 

[sbw1]

interesting. Is that because it requires more power and hence more RPM to get through the water?

I'm no expert in fluid dynamics, but I suspect it has to do with reducing the coefficient of sliding friction. There is a fine line between having the right amount of chop that allows the hull to lift a bit out of the water thereby reducing the friction and too much chop which creates head or following seas that slows the boat down while it powers through waves.