ill informed boat knowledge

[Mischief Managed]

Re: ill informed boat knowledge

BoatTest got 66mph running in salt water. In fresh water, I've seen as high as 67 on GPS but that was running with the cuddy stripped out in cool weather. Warm weather, half a tank of gas, couple of people, gear and it's a 63-64mph boat at lower elevations. In good conditions the same boat with the 525 runs 73-74. With the 600SCI, 80-ish. All 3 boats running "standard" prop shaft depth of 6" below the keel with no extension box. Is a pretty close comparison, and indicates that 10hp is worth well under 1mph in this particular boat, and/or there's way more than 100hp difference between the "425" and the 525.

A few years ago, a guy named Bob Lloyd did some prop shaft dyno testing on the 496magHO/Bravo X. Here's what he wrote:

We made a total of 4 pulls all within a couple of HP of each other. Final prop shaft HP was 387.8 at 5000 RPM, using SAE Standard correction method.

That seems to indicate the advertised power rating of 425 on the 496magHO is at the crank.

Perhaps Bob was using the wrong oil. :lol:

I ran your numbers and if you can get to 63 MPH with 387.8 HP, you will get to 73.3 with 525 HP, on the same boat, all else being equal. That's pretty interesting.

 

[tpenfield]

Re: ill informed boat knowledge

I wonder if "Ill Informed" would make for a good boat name :noidea:

 

[Don S]

Re: ill informed boat knowledge

I wonder if "Ill Informed" would make for a good boat name :noidea:

Sometimes it would make the perfect name.

 

[bassman284]

Re: ill informed boat knowledge

Use a torque wrench.


done now.

Lefty loosey, righty tighty.

 

[emilsr]

Re: ill informed boat knowledge

I ran your numbers and if you can get to 63 MPH with 387.8 HP, you will get to 73.3 with 525 HP, on the same boat, all else being equal. That's pretty interesting.

Maybe it's Mercury's marketing department that's ill informed.

 

[Bob_VT]

Re: ill informed boat knowledge

Sometimes it would make the perfect name.

Is that "Wet Storage" vs "Dry Storage"

 

[achris]

Re: ill informed boat knowledge

Yes !! There are open-ended torque wrench kits.

I'm going to get me a set of those...

(no, not really :facepalm

 

[smokeonthewater]

Re: ill informed boat knowledge

I know this statement to be true. How? Because we switched outdrives between two boats one afternoon. The B3 got out of the hole quicker, both times. And the B1 boat was faster on the top end (55+mph), both times.

Your results are hardly conclusive... To make a conclusive statement you would have to do that same test with all sorts of different props and then with various hulls and engines... For your particular boat and with the props you tested it may well be true but you haven't proven it to be true on all boats and engines.

 

[tpenfield]

Re: ill informed boat knowledge

:thumb:

My ill informed understanding . . .

The dual props versus single prop is that at the high-end, a single prop will get you more speed ( WOT ) due to less 'drag'. The dual prop will beat the single out of the hole. This spring I will have my first dual prop drives to see first hand.

I know this statement to be true. How? Because we switched outdrives between two boats one afternoon. The B3 got out of the hole quicker, both times. And the B1 boat was faster on the top end (55+mph), both times.

Your results are hardly conclusive... To make a conclusive statement you would have to do that same test with all sorts of different props and then with various hulls and engines... For your particular boat and with the props you tested it may well be true but you haven't proven it to be true on all boats and engines.

Well, if someone agrees with an ill informed statement of mine . . . I'm OK with that

 

[bcnul8tr]

Re: ill informed boat knowledge

Figured I would start this thread because I see allot of people saying things that are just wrong.

Fuel injection produces more HP than carburetor
4.3MPI puts out 220HP VS 4.3TKS puts out 190HP
5.0MPI puts out 260HP VS 5.0TKS puts out 220HP
5.7MPI puts out 300HP VS 5.7TKS puts out 250HP

:nono:

That is not entirely accurate, my 4.3L Alpha 4V puts out 225HP.
http://www.mercurymarine.com/repowe...ercruiser-products/plus-series/4-3l-alpha-4v/

 

[bcnul8tr]

Re: ill informed boat knowledge

Fuel injection, in a typical marine boat engine of the boats we are talking about here, will ALWAYS produce more power. quite a bit different.

:nono:

 

[QC]

Re: ill informed boat knowledge

Crankshaft horsepower ^^^^^^ :nono:

 

[TilliamWe]

Re: ill informed boat knowledge

Your results are hardly conclusive... To make a conclusive statement you would have to do that same test with all sorts of different props and then with various hulls and engines... For your particular boat and with the props you tested it may well be true but you haven't proven it to be true on all boats and engines.

My test was pretty conclusive, in my opinion. Nothing else changed on either boat, except the drive system was swapped. Each boat performed the same with each drive system. So you want to introduce multiple variables? What I did was prove with a constant. KIS (I'll leave off the stupid part, cause I don't think you're stupid. ) I like my results.
Ok, Bruce says the 2 blade dragboat props doesn't prove anything, so then why don't all go fast boats have dual prop drives?

 

[QC]

Re: ill informed boat knowledge

why don't all go fast boats have dual prop drives?

That actually works for me. Add in that Merc recommends B1s for faster boats and I am pretty convinced. Heck surfacing props are about half a prop, seems like the trend favors less stuff in the wawa for more speed

 

[emilsr]

Re: ill informed boat knowledge

My test was pretty conclusive, in my opinion. Nothing else changed on either boat, except the drive system was swapped. Each boat performed the same with each drive system. So you want to introduce multiple variables? What I did was prove with a constant. KIS (I'll leave off the stupid part, cause I don't think you're stupid. ) I like my results.
Ok, Bruce says the 2 blade dragboat props doesn't prove anything, so then why don't all go fast boats have dual prop drives?

At the risk of being argumentative (which is not my intent).....

What you did falls more in the realm of "anecdotal evidence", even though you did a great job of controlling variables and have valid test data. To prove that the Bravo I is ALWAYS faster than a Bravo III you'd need a much larger sample size than one boat.

Here's another example of anecdotal evidence:

A few years ago we had some dock neighbors (wealthy of course) who bought a new 38' Fountain Cruiser, powered by twin 496ho's and B1X drives. He wasn't completely happy with the performance of the boat, and wound up selling it and buying an identical boat with BIIIX drives (I did say they were wealthy). The new boat was actually a couple of mph faster than the old one at WOT. Not quite as controlled a test as you did, but as the boats were more or less identical except for the drives it was probably valid.

What does that mean? Who knows. I'm sure under most circumstances the edge in speed goes to the single prop drive, but there are exceptions.

 

[bruceb58]

Re: ill informed boat knowledge

Ok, Bruce says the 2 blade dragboat props doesn't prove anything, so then why don't all go fast boats have dual prop drives?

Depends on the boat weight and speed. I never said all boats will go faster with dual prop drives in case that is what you are thinking I said.

I am just saying drag boats use 2 blade props because only half the prop is in the water at any one time.

Volvo claims Duo-Prop drives are faster than single prop drives. Since they have probably done a whole heck of a lot more testing in boats than you, I or most people have done, I was just going by what they are saying. Not sure if anyone had done a Volvo Duo-prop vs Merc B3 testing. That might be interesting.

 

[QC]

Re: ill informed boat knowledge

Personally I think Volvo is saying "our Duo-prop drives are faster than our Single prop drives." Ever see a Volvo drive on any serious go fasts? Thought not

BTW not a knock on VP. I'd own a VP Duo-prop in a heartbeat. Heck, I like ALL Volvo technology. Those flippin' Swedes know a thing or two. You should see their latest truck transmission, 12 forward speeds of fully automatic beauty :thumb:

 

[bruceb58]

Re: ill informed boat knowledge

My test was pretty conclusive, in my opinion. Nothing else changed on either boat, except the drive system was swapped.

So what was the WOT with each configuration? Were they the same? How many different pitch props did you try with each configuration? If you couldn't select props to make the WOT identical, the test isn't valid.

 

[smokeonthewater]

Re: ill informed boat knowledge

yep my point is that the test showed results for the tests that you did but not for all boats... IE maybe a 28' cruiser with a single prop would be slower than the same boat with a duo... maybe a house boat would be different... maybe a 16' bass boat with 150 hp would be faster with a single prop but a 25' cruiser with the same power might be faster with two props.... You can say that as tested YOUR boat was faster so PROBABLY similar boats would have similar results but you can't say single prop is always faster than dual prop.

 

[emilsr]

Re: ill informed boat knowledge

Personally I think Volvo is saying "our Duo-prop drives are faster than our Single prop drives." Ever see a Volvo drive on any serious go fasts? Thought not

BTW not a knock on VP. I'd own a VP Duo-prop in a heartbeat. Heck, I like ALL Volvo technology. Those flippin' Swedes know a thing or two. You should see their latest truck transmission, 12 forward speeds of fully automatic beauty :thumb:

"Serious" go fast boats don't run Bravo drives either....not for long anyway. They won't handle the power that's available these days. Even the bulletproof Merc SSM 6 drive has been outclassed by the 1350hp engine that you can get from Merc racing. For that application they developed a new, even stronger drive (M8). Along with Merc racing and their NXT, IMCO, B-Max and maybe a few others have made upgraded stern drives that'll handle the 700+ hp engines that are more and more commonplace in that particular market. More than 500hp through a Bravo is a recipe for broken parts, particularly on a heavy boat.

....not that I'll ever be able to afford $500k worth of engines and drives in a go fast, but never hurts to dream.