Originally Posted by Tres

Thanks guys, Throttling is a thing of the past. Power management skills along with proper trim do the right job, most boats today are too fast for old skills. Teaching people to throttle turns most into animals on the water. Learned that lesson along time ago.

Originally Posted by troper

Have you every thought about on-line class for the basics?

Originally Posted by Too Stroked

Rick PM'ed me and I started to write something up on throttling for him. As ususal, I got way deeper than a simple PM would allow with a word count limit - and I didn't even finish! So I figured I'd share what I wrote for him with everybody instead. And remember, I didn't finish, so feel free to add.

Rick,

So let me see if I can explain throttling, or maybe more correctly “throttle control” to you as I’ve learned it over the years. As I said in my first PM, I’ve spent a ton of time in single engine high performance boats – mostly on Lake Ontario – and this leads to significantly greater amounts of air time than many folks get to see with bigger boats or smaller lakes.

My current boat is a 22’ Progression with a 240 HP Mercury outboard that runs 77.1 MPH on GPS. It’s probably one of the best handling small boats out there and loves rough water. But, it does require a good deal of skill to drive fast. One advantage to this particular boat is the way it’s set up. I have Latham hydraulic steering so I have immediate and minute control over direction. I also have In Control foot throttle and foot trim pedals at my feet. This allows me to keep both hands on the wheel and easily control the other functions at the same time. And throttling with your foot is actually easier than your arm if you ask me because nothing screws up one’s ability to throttle more than using the throttle lever as a means to hang onto the boat. And BTW, if your boat is not absolutely up to snuff mechanically, much of what I’m going to propose is semi-useless.

The first thing you need to understand about throttling is “thrust angle.” Unlike rear wheel drive cars, boats use the propeller and its relative angle to the hull to adjust the angle of attack of the hull – both side to side and up and down. This is important because when you have lots of positive trim, you’re not only pushing the hull forward, but pushing the bow up. Try trimming your drive up to the “trim limit” position while idling sometime. Now – with nobody else around – punch the throttle and quickly return it to idle. Watch the bow leap out of the water, then settle back down hard. And the same thing can happen when you’re up and running on plane. Oh, and now add in the ramp angle of the wave you’re riding up. See how thrust angle is important here? You always want to be thinking about where your drive is trying to push your hull because sooner or later, it’s going to get there.

Getting closer to actual throttling technique, let’s talk about water & wave conditions. Generally speaking, running with the waves / downwind will lead to more air time than running into the waves / upwind. The reason is the ramp angle of the waves. Running into them presents a flatter face which generally doesn’t to toss the hull up as quickly. Downwind however presents long ramps that give the hull plenty to launch off of. Why is this important? Because you’re going to have to do more throttling heading downwind. If you have to do any heading upwind, it will be shorter duration blips. Oh, and quartering seas are sort of a compromise between the two.

Now (finally) throttling. The first thing you have to remember is that water is incompressible and you can basically roller skate on it at 60 MPH or so. Each time your boat goes airborne and you don’t change the throttle position, your prop blades can rapidly accelerate due to the lack of resistance air provides compared to water. (RPM’s will rapidly climb too.) Then, when everything comes back down, the blades will hit that relatively solid / incompressible substance and bite into it. Think of grabbing a prop spinning at however many thousand RPM’s with a huge mitt and almost stopping it. Can you save driveline shock?

So if you don’t throttle, several things happen. One, your engine can over-rev and damage all sorts of internal components. Second, the rapid deceleration when you re-enter can twist all sorts of stuff in the drive. So it’s bad enough to over-rev something, but when you follow that up with an extremely rapid deceleration of the same components, you basically have the perfect storm. And I’ve seen some engine and drive damage from this very combination that would scare you.

So part of what throttling actually involves is minimizing driveline shock. If you were to graph engine RPM’s second by second in rough water, a well throttled boat would show more gradual changes in RPM’s. The slope would be less radical looking than a poorly throttled boat. Make sense? Oh, and by the way, being gentler to the driveline is generally easier on the hull and the passengers too.

What this actually looks like in a well throttled boat in rough water is adjustments to the throttle(s) both up and down as the boat leaves and re-enters the water. Ideally, just before a prop leaves the water, you will start to ramp off the throttle. Then, just as you re-enter the water, you want to pick back up at the exact new (slightly slower) speed you are now running. Then you can feed it the coals to pick up the speed you lost. Do you ever go all the way back to idle in the air? Remember, you want to match speed and RPM’s as you re-enter. So unless you stop in the air, I wouldn’t recommend it. Remember, a good throttle man doesn’t operate the sticks like toggle switches.

The best way I can describe this is like teaching somebody how to smoothly shift a car with a manual transmission. The smoothest drivers imperceptibly back off the gas just before they shift. Then they match ground speed to gear and engine RPM’s as they get back into the gas. The result is seamless gear changes with no head slap. Same goes for throttling a boat.

Now there’s a whole additional chapter I could write on momentum since there’s your hull, then a few other things (like fuel & passengers) that move around somewhat independently. That’s another day though and I’m sure Tres could go on for hours on it.

Hope that helps!

Tom