My God! It got wet!!

[Speed Racer]

Well, This late afternoon, I cut out of work early and did the big deed!
A bit chilly , but all things went well! One little oil leak, one little drippy water leak at one of the rudder bolts, but the boat floats, and runs and goes!!! 2 and 1/2 years later!

Photos here:

http://picasaweb.google.com/audiogg/FinalTouchesAndSplash#

I did not get to full throttle, but it really seems like it is under propped.
That, or perhaps the tach is off, but it seems to want about 3200- 3400 RPM to come up to plane, and really likes around 4200 at about 35 knots. ( I know the stupid GPS was set for nautical..do the math! :wink: )

Currently running a 12 x 16 and it did not seem big enough. The engine did not seem loaded at all, and in my view, spun up really quickly.

I would think that one would not really run around at 4 grand all day long cruising, right?

Can anyone give me some info on how your V-drive is propped!

I am tired, very happy, and love my new Donzi!!!

GG

[Just Say N20]

Congratulations! I can only imagine what you were thinking/feeling as you were driving to the launch, and then as you were unloading it off the trailer for the first splash. :eek:

I would agree with your assessment that it is under proped, but until you see what it spins at WOT, it would be just a guess as to what pitch you might need.

The boat looks fantastic! :worthy::worthy::worthy:

[gcarter]

One of the problems w/V-drives is the 1:1 transmission ratio.
I sized one of these for another member. Measure the tip distance to hull bottom distance and if it's more than 20% of the prop diameter, go up another 1" in diameter.
Also I'd probably go to an 18 pitch.
If you had room for a tranny w/a 1:1.5 ratio, then you could get serious w/it.

[BUIZILLA]

standard rule of thumb would be to keep the prop tip about 3" away from the hull, size your diameter for this first, and then adjust pitch accordingly

[BigGrizzly]

Welcome to the world of the living.

[Ghost]

One of the problems w/V-drives is the 1:1 transmission ratio.
I sized one of these for another member. Measure the tip distance to hull bottom distance and if it's more than 20% of the prop diameter, go up another 1" in diameter.
Also I'd probably go to an 18 pitch.
If you had room for a tranny w/a 1:1.5 ratio, then you could get serious w/it.

George and everyone,

So, this has me curious to learn something new, especially the part about the desired transmission ratio.

Assume for example an engine that tops out at 5000 RPM for its proper manufacturer-prescribed WOT performance. (It *could* rev higher, but this is not considered okay or good for the motor itself.) We want WOT to correspond with the max HP rating, and for that to occur at 5000 RPM.

In a ridiculously theoretical world, one could have a 5000:1 transmission that dropped the shaft rpm to 1 RPM at WOT. But, with a 4,435,200 inch prop pitch (and, hah!, no slippage), you could run at 70 MPH, even though the shaft was only turning 1 RPM. (EDIT: thinking more about this, I suppose this might illustrate you'd need a HUGE prop diameter for this setup to generate ANY real motion at all.)

Likewise, you could gear things the other way round, with a ludicrously high shaft rpm, and a ridiculously shallow prop pitch. (EDIT: with more thinking, this sounds like it would call for a very small diameter prop.)

These extremes, which sound convincingly like they would never work worth a damn, both suggest that other factors, having to do with how a prop interacts with water, the density of that water, etc, would dictate some optimum between the extremes. (Perhaps one way of thinking of that optimum is that it would minimize slippage, though I don't know if that thinking matters or helps. And I will admit, aside from spacing from the hull, ideal prop diameter is not something I have ever understood very well either, and I suspect that enters in here a lot as well.)

But anyhow, with all that sort of optimization thinking in mind, I am trying to understand the implications of George's statement above about the transmission. (Essentially, you'd be better off losing the 1:1 and dropping the shaft RPM down somewhat.)

My first inclination is that George's statement implies that there is probably some ideal range of shaft RPM at WOT for any propeller system to be optimized, and that (at least in this case), it means dropping the shaft RPM a bit below the engine's WOT RPM.

Is this the case? (seems hard to doubt, actually)

More important, if so, what's an optimum shaft RPM or range of RPM, and what's it depend on or not depend on? (And what does 'optimum' even mean in this case? Max WOT speed? I imagine the answers differ depending on what you are trying to optimize. EDIT: I also suspect it has something to do with sizing the prop diameter so it is both reasonable with the geometry of the boat, as well as providing decent performance over the range of engine RPM, not just WOT. But that is my speculation.)

Mike

(P.S. If anyone wants to do any specific examples, I would not object to a discussion of a twin-screw boat, deep V hull, motors that top out at 5000 RPM, and a 1.15 to 1 reduction through v-drives. I picked these numbers PURELY at random, I swear. ;) )

[Just Say N20]

(P.S. If anyone wants to do any specific examples, I would not object to a discussion of a twin-screw boat, deep V hull, motors that top out at 5000 RPM, and a 1.15 to 1 reduction through v-drives. I picked these numbers PURELY at random, I swear. ;) )
Uh-huh. Balloon text aside, I see TWO throttles and TWO tachs. . . .
I'm just saying. . . . :shades:

[Speed Racer]

One of the problems w/V-drives is the 1:1 transmission ratio.
I sized one of these for another member. Measure the tip distance to hull bottom distance and if it's more than 20% of the prop diameter, go up another 1" in diameter.
Also I'd probably go to an 18 pitch.
If you had room for a tranny w/a 1:1.5 ratio, then you could get serious w/it.

Aha!! But that too makes me wonder... The V-drive is actually not a 1:1.. it is a 1.29: 1.. So I read that as overdrive.. Right?? every 1 revolution of the engine/ transmission, is 1.29 on the prop shaft.. So to me, that would really indicate I need more prop to load things up a bunch more...
That image is small, but if you go here: and zoom you will see the ratio on the ID plate.....

http://picasaweb.google.com/audiogg/Powerplant#5291749990102638546

[Just Say N20]

Actually, I think you have it backwards. I think a lot of the ski boats have 1:1 ratios. I tried to zoom in on the image, and it got too fuzzy to read. If it says 1.29:1, the first number is engine rotation, and the second is prop shaft. If it says 1:1.29 then you are already spinning the prop faster than the engine.

My CARVER drives (straight inboard, not V-drives) are 2.92:1, which means the engine spins 2.92 times for the prop shaft to make one rotation. This allows them to run large diameter props with lots of blade area to be able to move a 20,000 lbs. boat.

If I'm confused, I'm sure smarter minds will jump in with a correction. :yes:

[Ghost]

Uh-huh. Balloon text aside, I see TWO throttles and TWO tachs. . . .
I'm just saying. . . . :shades:

LOL, they're on to me!! :)

Uh-oh, I also see I goofed up above in my reading, in that George was prescribing a 1:1.5 ratio, presumably to increase the shaft RPM, not a 1.5:1 ratio that would reduce it.

But either way that doesn't really change my questions on this front. I'm curious as all getout what is the advantage of the recommended transmission over a 1:1 direct drive that is propped differently.

Mike

[Speed Racer]

Ah!!

Good call.... Still Bigger prop though... right?

I have a call into my dad, who raced V-drives, offshore, jets, etc, for years, and need to get his definitive answer..

Hmmn so the V-drive is an Under-drive..

[Just Say N20]

The first shows what I think you have with the engine turning faster than the prop. I picked 18% slip for an inboard. A guess, but it worked out to be about your speed at 4,000 rpms.

The second box was for the same specs, but then prop shaft is turning faster than the engine. Big difference.

[Speed Racer]

The first shows what I think you have with the engine turning faster than the prop. I picked 18% slip for an inboard. A guess, but it worked out to be about your speed at 4,000 rpms.

The second box was for the same specs, but then prop shaft is turning faster than the engine. Big difference.

Wow!!
Very cool..! Seems pretty close too.. But we were looking at knots..

Get out the checkbook??

So, original question: What is everyone running??

Saturday, we compete for a trophy in the Seattle Yacht club opening day parade in the Classic Powerboat category...

Bunch of old farts in wood Chris-Crafts.. We'll see how that goes!
GG

[Just Say N20]

Wow!!
Very cool..! Seems pretty close too.. But we were looking at knots..

Get out the checkbook??

So, original question: What is everyone running??

Saturday, we compete for a trophy in the Seattle Yacht club opening day parade in the Classic Powerboat category...

Bunch of old farts in wood Chris-Crafts.. We'll see how that goes!
GG

If you ran 4200 rpms = 35 knots (40.2 mph), then backing off the throttle to 4,000 rpms would put you right around 38 mph. Pretty good guess.

I think it's funny you are asking "What is everyone running??" I think there might be one other person on the planet running your set up. Maybe. You are breaking new ground here!

And, wood Chris*Crafts can be VERY nice. :yes: And lots of work. But then your non-wood boat has been lots of work. The big difference here is their work could continue, and your big work is done. :shades:

[Ghost]

I thought that was very cool too. I re-ran the numbers (ever so slightly) with the exact parameters you had (using 4200 RPM) and converted the 35mph to knots using a factor of 1.15 mph/knot (based on 6076ft/5280 ft). Attached is what I got, which matches the slip calculation above at 18%. All the numbers were entered in as the given parameters except for the two circled in red, which were calculated from those parameters.

[Conquistador_del_mar]

Garry,
Congratulations on a successful first run! It looks great! The rudder housing looks wonderful with a new chrome job (or is that polished SS?), but the whole boat glistens like new as well. It looks like you are running a 1" prop shaft. If you are, send me an email with your address, and I will send you the two blade bronze/brass racing prop that I had custom built for my 18' Corsican V drive as something a little different to try. I had already sold the boat when the prop came back from the shop, and the buyer was going to "detune" the engine that I installed since it was too loud for his taste so he did not want it - that was 20 years ago. I will have to check the dimensions when I get to my shop today, because it might be a slightly larger shaft prop. Freebie of course. Bill
Dgill25960@aol.com or call me (903)786-6281

[Speed Racer]

Holy Cow Bill!!

Very, Very kind of you!!

If it is a 1" shaft, I would love to try it out!! A racey two blade would be killer cool!
Thank goodness the shaft and strut all ended up being VERY true.. NO vibrations at any speed.. Woo Hoo!!

I will PM you some information, and will make it worth your while to send that prop up for a test if the shaft size corresponds..

You all are great and I really appreciated this list!
GG

[chrisc2]

Way to go Gary! You made opening day with 2 days to spare!! I finished a restoration on a 67-18 and launched not far from where you did (Ballard?) back in 85. I put mine in at the north end of LK Union (public ramp just east of Gas Works). The only difference was I was trying to make it in time for the Hydros. I launched on Friday...All was good.:party:

[Speed Racer]

Way to go Gary! You made opening day with 2 days to spare!! I finished a restoration on a 67-18 and launched not far from where you did (Ballard?) back in 85. I put mine in at the north end of LK Union (public ramp just east of Gas Works). The only difference was I was trying to make it in time for the Hydros. I launched on Friday...All was good.:party:
Sweet!!!
Yep, that is exactly where we put in.. A long idle out to the lake Washington, then messed around out by the bridge!!

Where do you usually go out? We should certainly try to hook up!!
GG

[gcarter]

I was out working and it looks like I missed out on all the fun.
V-drives have all the usual issues and ineffiencies of any inboard and the best way to get to normal operating speeds, both boat and engine, is to slow the prop speed.
A two blade racing prop may work very well for high speed and probably very close to a 1:1 ratio, it should exhibit low drag w/2 blades and I never look a guift horse in the mouth. It should be a little different experience.

For all around cruising w/o wearing out your engine, the ideal would probably be a 1.5:1 ratio tranny (and, yes, that's 1.5 engine revolutions for every prop shaft revolution), and a 3 blade prop with as large of blade area as you can find. There's not as much "magic" in the "run of the mill" inboard props as there is in outboard/outdrive props.
An example of the inefficiencies of an inboard installation would be "WALO", a V-drive Hornet. It has a blown BB Ford w/about 900 HP and does about 80 MPH.

[chrisc2]

Garry (got sp right,sorry) - We operated out of the north end of the lake (WA) for years. We have been over in Kitsap in the salt water since 98. We have friends on the N end of MI that we see and stage from now. I was on the opening day and Hydro booms for over 20 yrs. Great place to operate a Donzis. 16's and 18's are perfect. Wait till you do a bonzi run between the bridges after the hydros are done on seafair sunday. This saturday afternoon might be a little lumpy come to think of it..

[Just Say N20]

Gary, I gues yu cn cal me Bil :shades:

[Conquistador_del_mar]

Holy Cow Bill!!

Very, Very kind of you!!

If it is a 1" shaft, I would love to try it out!! A racey two blade would be killer cool!
Thank goodness the shaft and strut all ended up being VERY true.. NO vibrations at any speed.. Woo Hoo!!

I will PM you some information, and will make it worth your while to send that prop up for a test if the shaft size corresponds..

You all are great and I really appreciated this list!
GG

Garry,
I had sort of remembered that my Corsican might have had a larger prop shaft. I checked today and I have two props for it - they are both 1 1/8" props. One is a 3 blade 20" pitch and the other is a two blade 16" pitch - that was the one I had offered to send to you. Evidently, I had a much different transmission or V drive ratios since the 16" would run 70MPH at about 5400RPM (and it would get there in a hurry). If you think you can modify them, just let me know. Sorry to get your hopes up before I had checked. Bill

[BUIZILLA]

where did the 1.29 ratio calculations come from?

[Speed Racer]

where did the 1.29 ratio calculations come from?

Top of the v-drive plate.. Under drive is what I am thinking.. But I will check that tomorrow... scroll back through the thread.. link to the page with the shot of the v-drive ID plate..

[Speed Racer]

Garry,
I had sort of remembered that my Corsican might have had a larger prop shaft. I checked today and I have two props for it - they are both 1 1/8" props. One is a 3 blade 20" pitch and the other is a two blade 16" pitch - that was the one I had offered to send to you. Evidently, I had a much different transmission or V drive ratios since the 16" would run 70MPH at about 5400RPM (and it would get there in a hurry). If you think you can modify them, just let me know. Sorry to get your hopes up before I had checked. Bill

Oh! Bummer!!
Well, it is very generous offer, and I appreciate it!
Now off to prop testing land for the next month or two!
GG

[rustnrot]

My five cents:

1. The v-drive 16 we redid here in GA has a new 225 hp 5.0L engine. It has a Crusader 1:1 v-drive box running 1 inch shaft. It uses, if I recall correctly, a 13x15 prop that lets it spin about 4600 rpms and GPS at 50.0 mph (that's it).

2. Spacers are available (they are made out of plastic) to allow larger bore props to fit on smaller shafts.

3. Your 1.29 ratio is almost certainly underdrive (shaft spins slower than engine), a friend has a Century Arabian with that same box.

4. Good luck with the 2-blade. We put a 2-blade on a Gar Wood speedster reproduction we made and it cavitated badly (not enough blade area and was nowhere near as smooth as a 3-blade).

5. The v-drive 16 here in GA has no trim tabs nor does it need them, it pops on plane fast and does not porpoise (of course the 50 mph top speed minimizes that issue).

[Conquistador_del_mar]

Oh! Bummer!!
Well, it is very generous offer, and I appreciate it!
Now off to prop testing land for the next month or two!
GG

Garry,
I think George probably nailed what you need with an 18", but you might even try a 19" with such a relatively light hull. I just checked ebay and the Seattle Craigslist with no luck. I know you will find the right one. Congratulations again, Bill

[Speed Racer]

Good calls on all fronts. Thanks for the advice.

Next stop, the prop shop!
GG

[chrisc2]

How did it go Saturday Garry?

[Speed Racer]

WwwwwweeeeeeTTTTT!

Too wet to play for me..
We pulled the plug on the parade when it started pouring.. Just seemed like not so much fun bouncing off of 300 other boats and trying to stay dry and keep the new carpet and upholstery dry... BUT went out and confirmed the same speeds and RPMs on Sunday!

[chrisc2]

You made it out there. That's what counts! While you guys were doing that (400 + boats) over on Montlake , there was a 2 day sailboat race (100+ boats) out of Shilshole and Shrimp opening on Hood Canal (300+ Boats). Lot's of people and stuff on the water for sure.

[Speed Racer]

Yep! it was either going to be Opening Day, or the Race to the Straits.. I probably should have picked the latter, but live and learn!

[chrisc2]

Weather wise that is a tough one to pick. There was a TON of boats out for the race to the straights.

[cutwater]

Congrats Garry! That's awesome.

[BigGrizzly]

Hey Cut, you have been asleep? What up?