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Old 17 January 2012, 17:13   #1
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Throttle control

I recently spent some time on the water with the Spanish Border Control. Cool guys. They were lending a hand on a shoot by allowing us to shoot from their RIB.
By "shoot" I mean photos, though they are very well catered for in the other shoot scenario.
We were tracking a HUSTLER which was touching 85 knots while we nudged 65.
This is a very physical photographic environment I hasten to add! "Haste" being a very operative word here.
Both helms were throttling off when airborne to prevent over rev and engine damage.......one job that on a two man race team the throttle-man obviously takes charge of.
Needless to say I experienced weightlessness for a very large proportion of the job........and have to say that in this environment the weightless aspect is very promptly greeted with lots of weight to the non fleshy elements of the human body. I was rapidly beginning to resemble a carcass.
I digress.
How many helms out there employ throttle control when airborne?
I have a good reason for asking as am developing a throttle system and it would be good to have some real experience feedback across the board, as it were.
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Old 17 January 2012, 17:35   #2
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Only when I'm expecting it, ie wave jumping, or able to. When in rough, a) sometimes it occurs when u least expect, or when you are trying to avoid being airborne b) it's hard when being thrown about if skippering alone.

85 knots!!!!!!

http://www.hustlerpowerboats.com/ WOW!!
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Old 17 January 2012, 17:55   #3
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These things cruise at 80mph in luxury cabin and heads trim, topping out at high 90's.
This was the 355 Slingshot in race trim. And thank the Lord for the foot braces.
A skiing black run doesn't come close to the work-out, honestly.
Funny thing is, you crave swell and chop.........it's not the speed, it's the air!!!
Out of interest, this was on the Gib Straits where cigarette boats earn their name as they do just that, still. Smugglers simply build the fastest boats they can to outrun Customs to drop cheap fags in Spain.
I didn't realize it still happened!
Despite the technical advances in their hulls and speed, they still launch from the same spots in Africa and aim for the same places in Spain.
For the border control it's mostly night-time interception using 65 knot armed RIBS, but it does appear that it's like shooting fish in a barrel. The smugglers don't employ any evasion techniques other than night and speed.........keeping to the same route.
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Old 17 January 2012, 18:14   #4
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this may seem like a stupid question but how come there is no rev limiter to prevent engines over revving in the first place?
also how much do you throttle back?
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Old 17 January 2012, 18:29   #5
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Quote:
Originally Posted by Nathan k View Post
this may seem like a stupid question but how come there is no rev limiter to prevent engines over revving in the first place?
also how much do you throttle back?
On almost all engines that will get you out of the water today there is a rev limiter.
The thing is that you don't want the engines screaming on the redline without load.
WOT with the props (not screws!) in the drink is the design brief in most cases for RIB mounted engines. Only when they get airborne "over rev" is catastrophic for bearings and friction surfaces. Valve bounce and all the other terminalities associated with heat, metal, balance and overstressed lubricant come into play. Momentum will also play a part in allowing an engine to spin longer than is necessary when without load even when rev-limited. This will happen when you're WOT and airborne. Piston rings are designed to operate under load, not freely spinning.
A few "over revs" every now and then are designed in but half a second every three or four for a sustained WOT over a minute are usually terminal.
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Old 17 January 2012, 18:30   #6
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Quote:
how much do you throttle back?
not at all....it hurts less when the boat lands and skips forward... rather than slamming down like a ton of bricks and breaking bones if you've throttled back.
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Old 17 January 2012, 18:31   #7
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also how much do you throttle back?[/QUOTE]

You throttle back enough to unload the engine.........with the props in the air ideally throttle back to the stop, but be back on full gas as you enter the water.
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Old 17 January 2012, 18:51   #8
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What you should hear when correctly operating the throttles whilst planing is a drop in engine note when airborne as apposed to the readilly heard "whaaa.....whaaa.....whaaa" of engines redlining as they skip the waves.
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Old 18 January 2012, 04:18   #9
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As a throttleman in a race boat it's something that I do all of the time - engines will rev past a limiter with the inertia of the engine making most limiters ineffective.

For example rev limit 7,500, you're going along at 5,000 as it's bumpy and all of a sudden the boat and prop leave the water and the engine is at WOT, the engine accelerates to 7,500 and the rev limiter cuts in but as the engine is accelerating hard it runs past the limit and hits 9 or 10,000! (V24's seem to be fairly bullet proof and the rule doesn't apply to them!)

As a turbo diesel throttleman the job is even harder as there is turbo lag involved, luckily the Yanmar BY260's a re great in this department and you have to be throttled back for quite some time to lose boost - the trick is not to push so hard that you're airborne for too long - it's slower anyway!
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Old 18 January 2012, 10:13   #10
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I throttle back and then back on again for the props entering the water, we get told to keep the power on but I'd rather be sympathetic towards the engine than screwing the nuts off em!
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