alpha ss

[mike o]

For my (95) 4.3lx 16.:wink: Santa.... do ya see this:angel:

[Lenny]

I believe you need a Gen1 transom assemble for this. Buizz would know. Or Jamie. I do know where there is one... :) (I mean another)

this one, oh and another... http://www.donzi.net/forums/showthread.php?t=54655

[mike o]

I believe you need a Gen1 transom assemble for this. Buizz would know. Or Jamie. I do know where there is one... :) (I mean another)

this one, oh and another... http://www.donzi.net/forums/showthread.php?t=54655saw it....:wink:

[Choprpilot]

I have one on my 18 Donzi Classic now and I'm thinking about upgrading to a bravo only because you cannot get any, yes there are no parts available from mercruiser any more for this drive. So If you bang one up or twist it off your sol and will have to replace it with another alpha or upgrade to a Bravo. If your curious to what I have in front of the SS Drive its a 468 BBC with 579hp.

[Lenny]

I have one on my 18 Donzi Classic now and I'm thinking about upgrading to a bravo only because you cannot get any, yes there are no parts available from mercruiser any more for this drive. So If you bang one up or twist it off your sol and will have to replace it with another alpha or upgrade to a Bravo. If your curious to what I have in front of the SS Drive its a 468 BBC with 579hp.

WHAT, I mean WHAT prop are you running behind that to stay at 5-ish grand ??? :eek:

30+ inches ???

I want a pic or two if you can post it :yes:

GPS ???

[mike o]

WHAT, I mean WHAT prop are you running behind that to stay at 5-ish grand ??? :eek:

30+ inches ???

I want a pic or two if you can post it :yes:

GPS ???..... spare rotors off the hel-o...:wink:

[chappy]

..... spare rotors off the hel-o...:wink:

That was funny.:tooth:

[mike o]

579hp to 205 hp. Easy living, Lenny, like going to the rest home.:)

[Choprpilot]

OK guys, Since you asked its a 26P round ear cleaver. I only had it up to 5400rpm and its still pulling. I probably should put on a life jacket. I think I can get this close to 6grand. Theres lots of torque especially when you hit the the go fast lever it wants to roll to the right but levels out nicely, and very stable at high speeds. I don't think I would want to try to turn it at 80mph plus, just my observation. I posted a pic of the motor last year but I'll have to dig it out and post it again here for you guys tomorrow.

[fogducker III]

OK guys, Since you asked its a 26P round ear cleaver. I only had it up to 5400rpm and its still pulling. I probably should put on a life jacket. I think I can get this close to 6grand. Theres lots of torque especially when you hit the the go fast lever it wants to roll to the left but levels out nicely, and very stable at high speeds. I don't think I would want to try to turn it at 80mph plus, just my observation. I posted a pic of the motor last year but I'll have to dig it out and post it again here for you guys tomorrow.


OK, am I retarded or am I not seeing this? You have an 18 with a 579hp, 468cid engine and an Alpha SS running a 26p "round ear" cleaver prop at 5400rpm...? and touching 80mph..........:confused:

I am by no means knowledgable in any of this but I am having a hard time comprehending this..........?

[Choprpilot]

You don't need gps to figure speed: rpm (5400) x 5 x pitch (26) divided by 7920 x .9 = speed ( 9.7 mph). If your ever up my way It would be my pleasure to show you. Yes, my Donzi is a sleeper the give away is the cam. I have been told it sound vicious. Plain and simple it hauls ass. Better yet bring your Scorpion and I'll give you a run.

[fogducker III]

You don't need gps to figure speed: rpm (5400) x 5 x pitch (26) divided by 7920 x .9 = speed ( 9.7 mph). If your ever up my way It would be my pleasure to show you. Yes, my Donzi is a sleeper the give away is the cam. I have been told it sound vicious. Plain and simple it hauls ass. Better yet bring your Scorpion and I'll give you a run.


I guess I wasn't clear with my post, sorry.......what I meant is with all that HP and RPM's and a big wheel I thought your MPH would be higher....:confused:

I have an honest 350hp at the prop on the same boat and while still on a learning curve and trying out props etc I am almost at mid 70's......

[fogducker III]

You don't need gps to figure speed: rpm (5400) x 5 x pitch (26) divided by 7920 x .9 = speed ( 9.7 mph). If your ever up my way It would be my pleasure to show you. Yes, my Donzi is a sleeper the give away is the cam. I have been told it sound vicious. Plain and simple it hauls ass. Better yet bring your Scorpion and I'll give you a run.

If I use the formula above for my application, in theory I should have got 67.95 with the 23P..........so why did I GPS at 74.1...?

5200rpm x 5 x 23 divided by 7920 x .9 = 67.954545.........:confused:

[cutwater]

If I use the formula above for my application, in theory I should have got 67.95 with the 23P..........so why did I GPS at 74.1...?

5200rpm x 5 x 23 divided by 7920 x .9 = 67.954545.........:confused:

If he's running a 1.5:1 ratio, and you're running a 1.36:1, the numbers work out. And yes, if he's making that much power I assume he is constrained by the rev limiter, not the inability to turn the prop faster.

[fogducker III]

I have new 1.5:1 so the math doesn't really work......... I was just curious...

Sorry mike O, have you found an SS yet?

[Choprpilot]

Your right about the rev limiter. I'm pretty sure I have a 1.5:1 gear the formula however is correct. but you can't dispute your gps. I certainly have enjoy this topic and the wealth of information everyone contributes. Have a great Christmas and a safe a happy New Year.

[mike o]

I have new 1.5:1 so the math doesn't really work......... I was just curious...

Sorry mike O, have you found an SS yet?Foggy. All good , We'll see what turns up. Might need some help to tweek one to a gen 2.:)

[cutwater]

I have new 1.5:1 so the math doesn't really work......... I was just curious...

Sorry mike O, have you found an SS yet?

Umm... that means you're getting 1.8% slip. I don't think that's very realistic. Are you sure your tach is correct?

With 10% slip, you would have to be spinning 5670 rpms to hit 74.1mph with a 1.5:1 ratio. Is that not above the rev limiter for the Scorpion? I don't know, maybe not. If it is... that leads me to ask -- Are you sure you have a 1.5:1 drive?????

[fogducker III]

OK, all this math, formulas and guessing is getting to me, maybe it is the buoyancy of the salt water that is confusing things???

I really don't know other than the fact that I am currently spinning 5200rpm with a freshly installed brand new set of 1.5:1 gears with a brand new tach that is working fine, with a Lazer II 23 pitch prop that is also fine and original, not changed or cupped or had an extra blade added (I know it is not the right prop for the boat at this point) and my GPS, which is also new, working and never been 'chipped'............ and I hit 74.1mph a couple of times, by myself in the boat with over a half tank of fuel, about a 1 or 2 foot chop, wind coming at me from my port stern side at about 5 knots on a sunny day with the temperature about 8 degrees C...........and I had an empty stomach.........does this speed/prop formula take into account anything other than "slip" and does it matter that I am running an Imco 2" shortie leg and a HUGE set of Dana trim tabs (set at a funny angle according to most) ?

In all seriousness, I think some rely a little heavy on theory and what "should" happen and don't think about the multitude of outside factors that effect performance, and at times, lack of it.

[mike o]

Foggy, Id lend you me lazer 2 25p, but it wont fit your bravo.:frown:

[fogducker III]

Foggy, Id lend you me lazer 2 25p, but it wont fit your bravo.:frown:

It won't fit even if I use the 1 1/4" hub kit sleeve I have? Or do you mean it is a solid hub?

[mike o]

It won't fit even if I use the 1 1/4" hub kit sleeve I have? Or do you mean it is a solid hub?....I bought it used from a wrench at the marina and he put it on. I not really sure if its solid or not. I know the vents are not plugged.

[cutwater]

In all seriousness, I think some rely a little heavy on theory and what "should" happen and don't think about the multitude of outside factors that effect performance, and at times, lack of it.

Agreed, but this is not theory. You're looking at a fundamental limit here. No way around it :wink:

[fogducker III]

Agreed, but this is not theory. You're looking at a fundamental limit here. No way around it :wink:

We have bastardized mike O's thread already, so might as well continue......:eek: :wink:

The problem I have about the speed formula and saying, "Your speed will be such and such because the formula says so"........is that it appears to not take into account the configuration of the boat....ie. weight, design, length etc etc.

How can one formula fit all??:confused: A formula as a basic starting point can be good, but it is only a STARTING point IMHO.

As I said, I believe, despite the exact science of math, there are MANY other factors that dictate what type of performance a boat has, not only speed but handling . I have seen it mentioned a number of times on this site that various boats "confuse" people because they do not do what they are suppose to.....

Being of limited intelligence, I tend to boat by "feel" and not theory, having said that, I will pick people's brains for info and their experience and if I can, pass some of my experience and info on certain things back. At the end of the day, I appreciate and understand most things people say, but doesn't mean I agree with it......:wink:

[cutwater]

Hey Jeremy, no offense intended. Like I said, your results are possible, it's just not very likely with what the experienced prop guys on this board have seen. I think that most real-world slip numbers are above 5% at those speeds, that's why I believe it's more likely a gauge error.

"Slip" is an all-inclusive scalar that will change depending on the type of boat, length, weight, X-dimension, etc. Those factors are already accounted for. Yes, it's close to impossible to accurately predict how fast a boat will go. That's not what I'm implying. :boat: :wink:

What is not debatable is that there is a physical limit to how fast a boat can go with a given prop pitch, drive ratio, and number of RPMs the engine is turning. Even the physically impossible, 100% perfect hull and prop design (0% slip) is constrained by this fundamental limit. Again, not debatable.

No matter what type of hull you have, whether 18 Classic or a 200 ft yacht - turning your prop, rpms, and drive ratio results in 1.8% slip. My only comment was that this is not a typical number seen in the real world, but if you're confident in the GPS reading & tach accuracy, then it very well could be correct! :wink: Okay, thread hijack complete :bonk:

[fogducker III]

Cutwater, points taken, understood, digested and agree..........thank you for not calling me an ass...........:eek::wink:

Now we just need to find mike O an outdrive........:yes:

Just for your info Mike, I had an Alpha I on my 21 Cruiser Inc and blew the bottom end, got an Alpha Gen II lower and with a couple of small mods fitted it onto the Alpha I upper and gimbal housing, Merc said it can't be done.....:eek:

All that is needed is to shave the inside "skid" plates on the gimbal ring and change the shift linkage out where the lower and upper meet.....done.....:wink:

Be VERY careful and re-adjust the trim limiter so the new Gen II doesn't make the Gen I upper hit the top of the Gen I gimbal housing, the mounting of the trim rams is different and makes extension longer........learnt that the hard way..........:shocking:

I have been running this set up on the 21' with a fresh 383 stroker, 21P Mirage Plus and doing just under 60mph all day long.........it is a VERY heavy boat and I carry LOADS of fuel, but so far, no problems.......:crossfing:

[Lenny]

A 25" pitch and 5200 and 74.1 @ a 1.5 gear ratio IS 10% slip.

Theoretical top speed on this with no slip is 85.3 mph.

...which I think is right on ...

http://www.mercuryracing.com/propellers/propslipcalculator.php

Jeremy, I am willing to bet that that 23 is a 25...somehow...

[fogducker III]

If a prop was re-worked would the new pitch not be stamped on it somewhere?

When I bought the Lazer II 23P from a guy off our local usedvictoria, he told me he bought it new on the advice of a local marine dealer, tried it once on his boat and it was obviously not the right prop for it so sold it, I have no reason to doubt the story but I agree that the numbers and performance of the prop are suspicious...?

I guess the proof will be in the pudding, once we have some boating weather I will be back out there with a handful of props and try them on the same day with as close to the same conditions as possible and try them all, remembering to write down the numbers...!

[cutwater]

A 25" pitch and 5200 and 74.1 @ a 1.5 gear ratio IS 10% slip.

We're not talking about a 25"... the numbers given were with a true 23". Hence 1.8% slip, not 10%. Again, I feel this would be an uncommon scenario at those speeds, but maybe I'm wrong. My boat only goes 60, haha :wink:... See original post - unless I am also missing something????


I really don't know other than the fact that I am currently spinning 5200rpm with a freshly installed brand new set of 1.5:1 gears with a brand new tach that is working fine, with a Lazer II 23 pitch prop that is also fine and original, not changed or cupped or had an extra blade added (I know it is not the right prop for the boat at this point) and my GPS, which is also new, working and never been 'chipped'............ and I hit 74.1mph a couple of times, by myself in the boat with over a half tank of fuel

[BUIZILLA]

is there an accurate prop calculator somewhere for twin or triple applications?

[cutwater]

is there an accurate prop calculator somewhere for twin or triple applications?

The regular calculator will approximately work, especially for twins, as long as the engines are turning the same rpms and the same type of prop. I would probably expect the slip numbers to be lower???

If the drives are mounted at different X-dims (like maybe triples) then you'd need a 3-D modeling program at that point to really understand what's going on since each power source would have unequal contribution to the overall slip. You would have to enter much more than just your pitch, RPMs, and ratio!

[BUIZILLA]

middle engine needs to come up one hole, outboard engines are right on..

Grizz, you got a PM