Saltwater vs Freshwater

verytricky · 08-10-2005, 01:56 AM

The density of sea water is about 1.027 g/cm3 at 15 degrees C, whilst the density of freshwater is about 1.000 g/cm3 at 15 degrees C.

The difference in density is about 3%

What difference does this make to the top speed of a boat?
What changes do you think are required for props?
Will the engine rev higher or lower?

Some opinions suggest that the added boyancy in salt water would make the boats 'lighter' and the added density will improve the efficiancy of the propellor, which would reduce the 'slip', increacing performance.

Ideas?

Ciao · 08-10-2005, 04:23 AM

Most race boats, and even more speedboats do not normally have their times calculated over a measured mile / kilo.
So the many guys that zap down i.e. Southampton Water with their GPS on and record xx mph watch the top speed - not the average!
To make your boat work at full speed – over two ways (one up one down) takes time, analysis, and dedication.
Forget all the B***S*** about density (Salt Vs Fresh), and you missed one there, the altitude of Coniston!
Make sure your engines are at their best; your hull is polished, and take the biggest run up possible before attempting the run.
My very opinionated view is this. “You know you have the right boat, set-up, props, before you go up to the lakes”

I have run 83 mph one way with 90 hp Yamaha - dont ask me about the other way!

michaelcaine · 08-10-2005, 06:13 AM

what about the other way?

verytricky · 08-10-2005, 01:33 PM

Quote:

Originally posted by Ciao

My very opinionated view is this. “You know you have the right boat, set-up, props, before you go up to the lakes”

Thanks for that.

I did notice at Windermere that the boat appeared 'sluggish' to pop nto the plane, like about 2 seconds longer to pop.

Secondly the revs on the engine were at 4700, whilst in the sea, in flat clam, I hit 4850. ( our engines are limited at 5000 )

I will be 'tuning' the prop after tests in freshwater on Monday, so that in fresh water I am maxing at 4950 rpm.

Polishing the hull? I had not thought of that! Would this be just the last 1/3rd of the hull?

What about oil for the gearcase? Can this safely be played with? For example the Bravo Six drive uses ol spray in a dry gearbox to achieve ( claimed ) 50hp more power due to not having fluid in the gearcase. Could you replace the oil with something else? Run lower oil level?

My best time to date ( at Windermere ) was 0.8 miles from the record. I need ( due to the 0.3% rule ) to go 1mph faster than my best time. So my need for speed is minor in actual terms....

verytricky · 08-10-2005, 01:36 PM

Conniston is 135 foot over sea level.

Matt · 08-10-2005, 02:46 PM

I have heard that ATF can give a little extra in the gearbox - but with a very short life for the box.

You could also thin the prop blades further - at the expense of sacrificing life.

Remove the alternator belt for the run? Dunno how much power an alternator draws?

Perhaps go to a 30 weight synthetic race oil in the motor?

Mix a bit of methanol in the fuel?

Take a large dump before the race?

And of course, make sure the hull is perfect.

doug · 08-10-2005, 03:18 PM

[[B]I have heard that ATF can give a little extra in the gearbox - but with a very short life for the box.

SHORT LIFE WHY?

Matt · 08-10-2005, 04:00 PM

In the words of Jay Smith, in 2002 (sometimes my memory works):

Quote:

For racing I like the "0" weight Anylsyn ( -5 pts for spelling ) I've even in tight races with inches needed to win used ATF but it is not load bearing to protect gears at all, a gear oil without the sulpher smell won't live long as the sulpher additive in lube oil takes up the space and shock of the meshing teeth ! For laking I like the 100 % Pennzoil Syn at Walmart..... I know you all get tired of me talking about the Pennzoil but I haven't found anything better on the market !

Matt · 08-10-2005, 04:03 PM

And, in my words, I reckon it's probably got feck all shear strength.

verytricky · 08-10-2005, 04:29 PM

Well the gearbox will only be in use for 10 minutes, so I think I will look into that. Also - regarding taking a dump, that does not work for a weight restricted class, due to Ana, I have to add 35 kg of ballast to the boat to make the minimum weight, all nicely packed under her seat!

Methanol in the fuel is illegal ( much like running E3 props to set the record initially, and hope the people at Windermere will not notice ( they did not apparently )) - No, I want to do it within the rules. I know some records are set using dodgy methods, but I dont want to play that way.

I have found the perfect oil for the engine. So that part is done and dusted!

I would like a tad more info on the oil for the gearbox, so I have a clear understanding of what you are saying:

To clarify:

According to the rules.....

951.6 Changes in spare parts are allowed as long as the driver, at races, can show that there is change from the manufacturer (a part number being replaced by another, etc.).
This would allow me to change the 'chip' as the new replacement chip has slightly better response. It is in fact the same part number, but the mapping has changed slightly at the 4500 - 5000 rpm range.

952.2 Sparkplugs may be changed for any other.

952.3 The propellers to be only Volvo Penta E2 duo props, these may be modified. The Volvo Penta E2 markings must be clearly visible on each propeller.

952.12 It is allowed to add rubber hose to the end of the exhausts.

953 - FUEL Fuel regulations according to U.I.M. rule 504.

So - any idea on the 'add rubber hose' to the end of the exhausts?? This seems VERY odd, but it is in the rules as allowed. Why?

Wacky Racer · 08-10-2005, 04:41 PM

Years ago I purchased a Astrs GTE when I asked why the Cavalier SRI produced more BHP from the same engine, I was told that it was because the exhaust was longer, I may be barking up the wrong tree, any body else got any ideas ???????

JamesM · 08-10-2005, 04:50 PM

Quote:

Originally posted by verytricky
Also - regarding taking a dump, that does not work for a weight restricted class. I have to add 35 kg of ballast to the boat to make the minimum weight

Dude that is one big dump!!!! How many flushes to get rid of that one?

JamesM · 08-10-2005, 05:00 PM

Quote:

Originally posted by Wacky Racer
Years ago I purchased a Astrs GTE when I asked why the Cavalier SRI produced more BHP from the same engine, I was told that it was because the exhaust was longer, I may be barking up the wrong tree, any body else got any ideas ???????

Was the inlet manifold different on the Astra due to less clearance between the motor and the bulkhead?

The 16v motor made the same power in the Astra as it did in the Cavalier!!!

jw. · 08-10-2005, 07:48 PM

Quote:

Originally posted by verytricky
Well the gearbox will only be in use for 10 minutes,.....

How about a dollop of grease. Mix it with a small amount of gear oil so it slops about a bit. Feck all cooling though.

jw. · 08-10-2005, 08:01 PM

Quote:

Originally posted by verytricky

According to the rules.....

952.3 The propellers to be only Volvo Penta E2 duo props, these may be modified.

If E3's are better, why don't you tap the E2's with a hammer?

verytricky · 08-10-2005, 11:17 PM

We are allowed to 'work' the props. So we can set the props to match the water and conditions.....

Cookee · 09-10-2005, 09:43 AM

Why not move the 35kg of ballast to the back of the boat - surely you can put the extra weight where you need it?

verytricky · 09-10-2005, 12:00 PM

Quote:

Originally posted by Cookee
Why not move the 35kg of ballast to the back of the boat - surely you can put the extra weight where you need it?

Within the cockpit ot cockpit liner.

( besides, I like the balance left vs right when its under Ana's seat...)

I could get a steal engine mount I suppose.....

FrenchPhil · 10-10-2005, 09:34 AM

Ciao, 83mph with a 90hp !!!

You gotta give me your setup. I won't tell anyone ...