12.5 mph

[Ball Racing]

Video!

http://www.youtube.com/watch?v=R5IlXw0OBak

http://www.youtube.com/watch?v=scCSLe6Kc3k

[ILikeRust]

Suh-WEET!!

Man, that boat looks fantastic.

My only complaint is I couldn't hear the A4 enough over the other boat's motor.

But she looks great. How does she handle a chop? Have you had her out in anything like that yet? Looks like a right stout boat.

[Ball Racing]

Seems to like the chop, just chug on thru it..
I was in wome white caps the other day, 20mph wind at least 2+ footers,
just making spray, and ride on..(you can get wet doing that )
Every now and again when you found the right series of waves you could hear the prop maybe slip a little, then just go to the next set.I basically could go full throttle into the seas
I turned around and following seas are not as fun, I decided to stay at hull speed, except for when you 'surfed" down a sea and almost doubled your speed.
But you have to counter steer, and watching water pushing up at the stern , and feeling the boat get shoved down,,,is not as much fun as head into..

I know, that I don't want to be in the boat, in the weather it would take to dip the bow........
Or rather the boat can take more than I can

[Gordo]

Great job man!!! I'm a builder as well...I wonder if you did a build page anywhere? I hang out at Duckworks and the huys there would love this boat!!!

[sastanley]

Daniel,

So..do we have a tach on this thing? What RPM are you up to with your latest improvements to achieve 13 MPH?

[Ball Racing]

2,550 RPMS On my teleflex brand tach.
Thats with a old design 3 blade 11x7 prop.
I want to try a 3 blade 11x6 Michigan Dyna Jet that should put me @ 2,800 RPMS which I think would be plenty..
I feel I need to get higher into the rpm band to get more HP, right now I am only using 20hp. 3,000RPM is suspose to be 25hp.
To run like I was in that video, was MAXED Out, and I only run it like that for maybe 4 minutes at the time before I lift back to hull speed.
I don't want to burn the motor up.
It has more throttle lever left, Just can't get more rpms.
It take a rich setting to run those max rpms.
If I idle around for more than 5 minutes with that power setting she smokes badly from the extra fuel.

[ILikeRust]

Which makes me wonder - what is the max RPM that the A4 should be run at for any period of time?

It really doesn't seem like a very high-revving engine to me, so I'm a bit paranoid (maybe overly so) about revving it up too much. In my recent test-running, I will give the throttle a little blip to give it a quick rev, but only for a second or two. Then I quickly bring it back down to idle.

Like I said, maybe I'm being overly paranoid, but I don't like to rev it too high - although the engine does seem to be very stoutly built, it also doesn't seem like it was meant to be much of a high-revving engine - certainly not for any period of time, anyhow. Maybe a short burst now and then.

Eh?

[joe_db]

My original A4 ran 100% throttle from Cape May to New York and did fine.

Which makes me wonder - what is the max RPM that the A4 should be run at for any period of time?

It really doesn't seem like a very high-revving engine to me, so I'm a bit paranoid (maybe overly so) about revving it up too much. In my recent test-running, I will give the throttle a little blip to give it a quick rev, but only for a second or two. Then I quickly bring it back down to idle.

Like I said, maybe I'm being overly paranoid, but I don't like to rev it too high - although the engine does seem to be very stoutly built, it also doesn't seem like it was meant to be much of a high-revving engine - certainly not for any period of time, anyhow. Maybe a short burst now and then.

Eh?

[ILikeRust]

My original A4 ran 100% throttle from Cape May to New York and did fine.

Do you know what RPM that was?

Also - I note you say your "original" A4 - is that because you had to replace it after that trip?

[joe_db]

I had no tach them but I would guess around 2700 RPM +/- a hundred or so.
The engine lasted a long time after that, but salt water ate it eventually. A4s don't wear out for the most part, they rust out.
I am on #3 right now I expect this one to be good for at least 20 years.
#1 1973 to 1994
#2 1994 to 2011 (not a very good one when I got it)
#3 2011 to ????

My engine use is around 100-300 hours per year.

Do you know what RPM that was?

Also - I note you say your "original" A4 - is that because you had to replace it after that trip?

[edwardc]

Although the specs list the max RPM as 3500 (??!!), in our recent meet-up with Hanley, Don Moyer said the engine is happiest running about 2000 to 2200 RPM. Running above that for long periods of time puts a lot more stress on the engine.

I recently measured my back pressure, and under load it begins to go up rapidly above 2000 rpm.

It's a concern to me, as I'm usually running at 2400.

[Ball Racing]

Is there a backpressure point, that has shown damage?
My exhaust is 7 foot long straight shot after riser-water entrance, no muffler.

The more rpm, the more air in, the more has to leave, the higher the rpm the more HP made, so the more btu's made, the greater volume of spent gases,
so all those things will make for more pressure in the exhaust,
but that is relative to the rpm curve, and all makes of engines in general.

I thought the exhaust back pressure gauge was just to make sure the exhaust wasn't rusting up, and collecting minerals, and salts?

In the auto style engine world, to low of rpm, with lots of throttle, will just burn it up, and wear out the rod bearings.
higher rpms with less load is better than low rpms and high load..

[edwardc]

According to Don, anything over 2 psi for extended periods is a cause for concern. But rather than hijack this thread, I'll start a new one on backpressure.

[sastanley]

Daniel, thanks for the info. I, too, have always wondered if there was any real reason to try to get the motor to its 3,500 max RPM, & it sounds like there isn't. Us sailboat guys have the same issue you are noticing that there is xx amount of throttle and that is as fast as it goes, since we are obviously limited by hull speed. When the prop & hull are clean, that isn't very much..maybe 35% or so and after that she just gets noisier from the throttle being opened farther & more fuel being jammed down (up) its throat, but no more RPMs.

I know I don't go spinning my car up to it's 8,000 RPM redline every day.

At 11+ knots I wonder about a bigger intake horn and maybe some ram air for your A4!!

[joe_db]

AFAIK if you want to get useful work out of an A4 in the 3000-3500 RPM range, you need the reduction gear.

Daniel, thanks for the info. I, too, have always wondered if there was any real reason to try to get the motor to its 3,500 max RPM, & it sounds like there isn't. Us sailboat guys have the same issue you are noticing that there is xx amount of throttle and that is as fast as it goes, since we are obviously limited by hull speed. When the prop & hull are clean, that isn't very much..maybe 35% or so and after that she just gets noisier from the throttle being opened farther & more fuel being jammed down (up) its throat, but no more RPMs.

I know I don't go spinning my car up to it's 8,000 RPM redline every day.

At 11+ knots I wonder about a bigger intake horn and maybe some ram air for your A4!!