Boat horsepower

Darrell

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I had a nose around one of the boatyard/storage yards today and some of the boats there are packing some serious horse power.

Now, I am no expert but one boat, not huge, was loaded up with 2 x 300hp Mercury engines. This is more power than a Porsche but the boat doesn't go as quick as a Porsche.

Can someone tell me why.

Cheers.
 

Howard

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Drag in water ( hydrodynamics ) is much greater than drag in air ( aerodynamics ) ...

The boat will weigh a lot more than a Porsche too.
 

MangoMan

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Not only as Howard states, but they are measured at the crank usually, and to my understanding that is rated at about 6500 rpm. but the max you will get in the water will be about 3500 rpm. so in real terms at those revs and at the prop you are lucky if you're getting 150hp! (FOR BOTH) And have bugger all torque to speak of.

This is what I have been led to believe from years ago when I did a lot of Ski-Boating in Zim, if I'm wrong, I will stand corrected.

Cheers.
 

lxi

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Some years back I watched F1 power boat racing in Portugal.

The noise was awesome, the performance even more so.

At that time I had a TVR Cerbera 4.5 - hooligan machine. 0-60 3.9 seconds, 0-100 8.0 seconds. These boats were faster - I seem to remember 0-60 took less than 3.5s

Absolutely no idea how they get that much "traction" in water with a propeller !!
 

Howard

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F1 offshore boats have serious ( 4000+ hp ) , and run surface piercing props , they will do upwards of 150mph.

If you watch the videos of them racing you will see that only the last 5 feet of the hull is in the water when they are up to speed , hence minimising the drag. The boat is trimmed that way.

Below is a good illustration , look at it accelerate !! :eek: Looks evil from behind at 1.02 , the roostertails are from the SP props.

[YOUTUBE]5ORjZ8Dpa7k[/YOUTUBE]
 
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Howard

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Yeah , its turbine driven ..... those guys have got balls of steel ..

200mph on water will feel like 600mph in a car !

Actually 0.36 onwards is a good illustration of what i mean by only the last few feet of the hull in the water at speed to reduce drag.

[YOUTUBE]KqsNyXIEIwg[/YOUTUBE]
 
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Darrell

Darrell

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Howard,

I thought that the boats were alot lighter than say, a Porsche for example.

There was a 2008 Cigarette boat here in the summer (Google it) and all I can say is wow!!! These boats are banging out over 1000hp.
 

Howard

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Cigarette boats originally were designed by Don Aronow and were the boat of choice for drug dealers to run in and out of Miami.

He was killed by one of them some years back.

I've been in a cigarette and i agree , they are incredible boats.

Cougar Marine ( UK based ) make some pretty similar boats , Steve Curtis who owns it is an F1 champion.

The boats are surprisingly heavy , they have to be built strongly to withstand the pounding of the sea at high speed , we're not talking about a mad offshore circuit racing hydroplane type boat are we ? those are pretty light .... the 300hp outboards weigh a fair old bit on their own !
 

Mudster

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F1 offshore boats have serious ( 4000+ hp ) , and run surface piercing props , they will do upwards of 150mph.

If you watch the videos of them racing you will see that only the last 5 feet of the hull is in the water when they are up to speed , hence minimising the drag. The boat is trimmed that way.

Below is a good illustration , look at it accelerate !! :eek: Looks evil from behind at 1.02 , the roostertails are from the SP props.

[YOUTUBE]5ORjZ8Dpa7k[/YOUTUBE]

That's awesome.
 

st13phil

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A couple of great vid's there, Howard :rock:
... those guys have got balls of steel ..
You're not kidding :eek:

Personally, I've always though the offshore racers are certifiable...
 

davidjpowell

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I had a old Sunbird Cuddy, which was a 19ft american boat with a 5.3 litre OMC V8. Sounded fab, bounced around a lot and drink fuel faster than a fish could drink water...

Fastest way to burn money...

Think it was about 1400 KG. Certainly felt like it trying to drag it out of the water with a 1.8 Petrol Laguna. The head of office drove by shortly after I had pulled it out once, I was hoping he could not smell the clutch because I certainly could.
 
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Darrell

Darrell

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There are some local guys here with some serious pieces of kit.

In the summer, all the Mastercrafts and Ski Nautiques come out from the woodwork, all rigged up with the big wakeboard towers and Barry speakers.

The Athenians all come over in their huge RIBs all kitted up with twin 250's & 300's.

Funnily enough the owner of the boatyard told me that the best way to enjoy a speedboat was to use someone elses!!
 

Howard

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They say the happiest days of owning a boat are the day you buy it and the day you sell it ...

Saying that , if people didn't have boats my family would be out of a job , so boats are good as far as i am concerned....

Here's what happens when it all goes wrong at 150mph ...

[YOUTUBE]h6uNwQe4lRU[/YOUTUBE]
 

janner

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Here's what happens when it all goes wrong at 150mph ...

"ya'll right buddy"
"Yup"
"We're up the right way brother"
"Ha-ha-ha"


Brilliant.

What I love about boats is there's no upper limit to what you can spend.

I'd like to have a go in one of these bad boys.
http://www.youtube.com/
But not any of these

@ MangoMan
Boat engines are generally designed to have lots of torque so produce power lower down the rev range than cars. If the engines are rated at 300bhp then you'll get 300bhp, probably at about 4500-5000 rpm, which is what you aim to run them at flat out. The Mercury 300bhp engine is based on the 5.7ltr small block Chevy car engine.
 
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tim.100

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.....my understanding that is rated at about 6500 rpm. but the max you will get in the water will be about 3500 rpm. so in real terms at those revs and at the prop you are lucky if you're getting 150hp! (FOR BOTH) And have bugger all torque to speak of.
...
Cheers.

In that case your boat would have to be re-prop'ed, with new props of a lower pitch so the engines could just achieve red-line but not more.

Search 'Re-prop forum ' for endless debates!
 

MangoMan

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Yeah sure you could re-prop, but that would only mean that you would still be doing the same speed at the higher revs. The only thing you would achieve is more regular stops at the pumps......

And Janner, a friend of mine had exactly what you are refering to, he played with props etc. He still only managed around 3200rpm. flat out, and that was on a mirror calm lake!

Don't forget here chaps, I'm talking about your everyday Ski/Pleasure craft of the 18 to 24 foot region, not racing boats.
 

janner

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There must be something wrong with the engine if it only revs to 3200 despite playing with props.:dk:
Maybe the bottom needs a clean and all the excess weight removing from inside?
 

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There must be something wrong with the engine if it only revs to 3200 despite playing with props.:dk:
Maybe the bottom needs a clean and all the excess weight removing from inside?

Thats sounds errrr terrible.

Where can I have a passenger ride in an F1 boat? I would love to have a go. I like going fast you see.:crazy:

I have never been above 187Mph while driving so I want to break that 200mph barrier.
 

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