WOT

[tunaticer]

I read volumes of posts where people are ever so concerned about their WOT and speeds and holeshots, but I am left wondering how many people drive thier boats at WOT?


Is there a reason why WOT should fall within a 500 rpm range when for safety on the water you can achieve about half of that figure?

Holeshots I can understand as there are times when you need that downright grunt to get yourself out of trouble or to avoid it from finding you.

From my perspective, you can adjust your boat to acheive perfect WOT but if you run it at half of those RPM you have simply wasted that exercise or am I purely wrong?

When I last had a open water boat I would head out accross the bay and offshore running at about 2800 to 3200 RPM and be comfortably cruising at 25-30 knots depending on conditions. Running a 140 Zuke like that for a couple of hours each way each trip, would that damage the motor if it does not reach the 5000 rpm?

[FishHunter]

Getting the WOT rpm right normally means you are not over propped or under propped and should have a reasonable cruising speed in the most efficient rpm range.

Its exactly like gearing in a car except that one gear has to work from pull off to top speed.

[wags on the water]

I'm sure most need to get the adrenalin rush of going flatout, but it hurts the wallet too much. I'd prefer to get to spot X with plenty of fuel in the tank to visit Spots Y and Z rather than getting to spot X in 5 mins. I have only run the boat at WOT once to find out exactly how fast it goes....then seeing how much fuel was being used at WOT shocked me.:o :o So it's 1/2 to 3/4 throttle for me now.:)

Cheers,
Wags

[STUIE63]

WOT is important so you are not lugging your engine . not that people have to drive their boats at WOT . but it should be able to reach it . my boat when supplied didn't reach it and after some prop testing the boat ran quieter , had better bow lift , had better holeshot and better fuel economy .all for the loss of 1/2 a knot of speed. I even know a boat that porpoised and with a change of prop it stopped . Both this boat and mine were not a radical prop change but the same style of prop just 2" smaller in pitch .
to sum up if your motor is not reaching WOT then you should get a prop that will get bit there or you are damaging your motor and it will not last as long as it would otherwise . it is not about cruising all the time at WOT
Stuie

[Chimo]

To 'decoke' (blow any build up out) of a couple of old 2 strokes I tend to run them close to flat stick for a short while after running mid range for most of the time.
So far they seem to be happy enough with "a run" once in a while...........and I get to check that they are not overheating and everything is going up and down as it should be.

Cheers
Chimo

[rosco1974]

not sure bout other's but wot in my boat i hit 5700rpm and 35 knots but i sit on 4500 and 25 knots plenty fast enough for me
cheers rosco

[Seahorse]

I Usually Sit On 20/23 Knots. Wot For Me Is 30knots.
Thats In 455 Tinnie With A 50 Yammy 4st.

Cheers
Greg

[tunaticer]

Thanks guys, as I suspected, few of us ever need WOT for our travelling.

I suppose the next big question is running a motor at 1/2 throttle and easily on the plane would the correct prop be one that acheives WOT recommended rev range or would a different prop / diameter / pitch one that gives better economy / performance at that 1/2 throttle cruising speed range be a better proposition for the motor and running costs?

What delivers the WOT target might not be essentially the best prop at normal cruising speeds.

[snodger 08]

The way it was explained to me when setting up the Galey was that if you had the balance right at WOT, then it would be pretty close to the mark through the whole range.
I think (I am no expert) that its mainly a matter of getting the balance right between the prop and motor, taking the strain off the motor. Apparently it not only takes the strain off the motor at WOT, but through the whole range.
Hmmm coulda explained that better ::)

[Moonlighter]

Here's what Ken Reeves who runs a US company called "The Prop Gods" says in response to this question:

"Someone writes:

“I don’t think I really need to test my props by going to WOT, I don’t run fast and just like to cruise”

A common misconception is if you are not a full throttle user (WOT), that the props that came with your boat are the proper ones. Running at full throttle is not something that any of us do often, but just like your car transmission selects the right rpm, a good prop does that too. Too big a prop and you will be “lugging” the engine in cruise. But the testing requires WOT (wide open throttle) to see if you are propped correctly for long engine life.

Here is how to tell if you are propped correctly. This may rattle you to cavitate your engines but it'll be OK....

1. Load the boat down with 50% gas and a light load for fishing cruising, etc
2. Find a very flat piece of water a mile long and bring your trim tabs all the way up.
3. Trim your engines "in" and take it up to full WOT and start trimming up
4. Keep trimming up SLOWLY a bit at a time, letting the boat catch up to the setting...until the engine starts cavitating - losing speed ( you can't hurt it - all new engines have rev limiters)
5. Now drop it back down a bit until it "bites"
6. Now look at your rpm...- it should be in the top half of the mfr's recommended top end rpm. For example, the Verado’s range is 5800-6400 rpm. Therefore I should be at least 6100, 6250 would be ideal. But don't get hung up here, anything over 5900 rpm is ok, you won't be hurting the motor. A few more hundred rpm may get you a bit more speed though. But less than 5800 is going to do long term damage to the motors. It will cause the motor to add gas to the oil, raising the oil level and diluting the protection the oil gives the motor. Eventually the crank will fail and it will not be warranty.
7. Fill out the PDF sheet below so you can compare after you are completed.

compare the results on a prop slip calculator - at WOT and cruise you should be less than 10%---> go here: http://www.rbbi.com/folders/prop/propcalc.htm

It should be noted that prop changing is not a magic cure-all - all you can do is try to get your props up near the upper range of mfr WOT and that's about it.

Too many people think changing props is like adding Nitrous or 50 more HP...not so....it's fine tuning in my opin, and for me never been worth more than a few mph or gph when changing a pitch up or down...However, many props are different.... some are smoother than others..others allow you to dock better ....it's not just all about hard statistics....I personally run a prop that gets a bit worse mpg and less top end but it "feels" better than all the others I tried....Don't get hung up on specs searching for the "holy prop grail".

Size depends on what you find above, but three of the best props for < 35 feet are Merc’s Tempest Plus, the Revolution 4 (4 blade) and the new Enertia. Most boats come with a Mirage plus as it is a good all purpose prop."

Ken Reeves of Propgods.com."