Surface drive Tech
04-17-2002, 08:42 PM
#1
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Surface drive Tech
I am looking for some detailed info regarding surface drives.
For arguments sake assume that the boat in question is a 20-30' boat with a single 450hp motor, set up for an Alpha/Bravo outdrive.
A) How would you estimate the 'X dimension' for a surface drive?
B) What are the effects of having the prop further behind the boat? (is that X or Y Dim?
)
C) With a surface drive, what trim range would you want/need?
D) How Deep would you want the prop when trimmed down? [Combination of Questions A&C...)
I hope I'm not annoying anyone, I just have no source of information for this kinda stuff and I can't find ANYTHING online referencing even the X dimension of an Arneson or any of the other surface drives...
Without asking for opinions on the quality of the concept , I'm trying to figgure out what would happen if you had a surface drive that mounted to your IO gimbal, basically...
If however you absolutly know thats the dumbest thing you've ever heard, let me know why, but please be nice
--Adam
[cheap through necessity, and too much time on my hands]
For arguments sake assume that the boat in question is a 20-30' boat with a single 450hp motor, set up for an Alpha/Bravo outdrive.
A) How would you estimate the 'X dimension' for a surface drive?
B) What are the effects of having the prop further behind the boat? (is that X or Y Dim?
)C) With a surface drive, what trim range would you want/need?
D) How Deep would you want the prop when trimmed down? [Combination of Questions A&C...)
I hope I'm not annoying anyone, I just have no source of information for this kinda stuff and I can't find ANYTHING online referencing even the X dimension of an Arneson or any of the other surface drives...
Without asking for opinions on the quality of the concept
, I'm trying to figgure out what would happen if you had a surface drive that mounted to your IO gimbal, basically...If however you absolutly know thats the dumbest thing you've ever heard, let me know why, but please be nice
--Adam
[cheap through necessity, and too much time on my hands]
04-17-2002, 09:37 PM
#3
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I am in the process of building a 615 hp arneson asd-6 donzi (22 classic). I am a marine engineer and have given thought to what you describe. It is not a horrible idea but sure not that easy. Aside from all the custom machining and actually making this thing the hardest part is making it shiftable. An alpha style dog cluth is worthless, a Bravo cone clutch type mechanism is used with a 90 degree bevel gear and would be real tough to adapt to a typlical arneson style gear or chain drop. It seems to me you would need some sort of real clutched tranmission. If it was inside the boat it sort of defeats the purpose because it just doesn't bolt on. If it is outside the boat I have no idea how you ever could manage that attached to a alpha/bravo style gimble. IT just would be real tough considering the size of a clutched style transmission. Then there is the strength issue of the actual gimble housing....basically the way I see it, and I have looked into it pretty hard, if you want a surface drive an arneson is the easiest and cheapest option. Oh BTW way they did make a surface drive that just bolted on to your gimble...but no one bought it.... the Blackhawk
Chris
Webb Institute
Chris
Webb Institute
04-17-2002, 09:49 PM
#4
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Wasn't the blackhawk more of a 'really high X' outdrive?
And if it was cheaper then Id imagine it would have sold better... Then again I have quickly gone from 'Mercruiser Good' to feeling that trust is proportional to soreness of rear end (which is linearly related to emptyness of wallet) when it comes to Mercruiser.
Lets assume for a minute that you had the tranny issue resolved, and had a good idea how to attach it to the gimbal...
I have to assume that if the X dimension was 0, that wouldnt work well? If it would, Im happy as hell
Thats the part that I'm currently working on
As to the weakness of stock gimbals- How weak are they?
--Adam
PS I have an 86 454/alpha boat, so you can understand why I am particularly unhappy
And if it was cheaper then Id imagine it would have sold better... Then again I have quickly gone from 'Mercruiser Good' to feeling that trust is proportional to soreness of rear end (which is linearly related to emptyness of wallet) when it comes to Mercruiser.
Lets assume for a minute that you had the tranny issue resolved, and had a good idea how to attach it to the gimbal...
I have to assume that if the X dimension was 0, that wouldnt work well? If it would, Im happy as hell
Thats the part that I'm currently working on
As to the weakness of stock gimbals- How weak are they?
--Adam
PS I have an 86 454/alpha boat, so you can understand why I am particularly unhappy
04-17-2002, 10:50 PM
#5
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Well you would need a drop. You are going to need the center of the prop shaft to a a couple inches ( this is really rough estimate) above the bottom of the boat ( in neutral trim). In reference to the stock gimble. I really have no idea. First of all I would not even consider the alpha gimble. The alpha was designed for 4 cylinder engines and has been modified and adapted over the years. Basically they just kept throwing band-aid fixes on it. Even if you had a Bravo gimble we are still talking some really wild forces on it. Putting aside the fact you have 450 hp ( or that is at least the reference) you are going to need to have probably in the area of 12-18 inches of a drop. That is going to make one hell of a lever arm on that gimble. I guess a convential drive is as much of a lever are but we are talking about a substantially larger, heavier, and longer drive.
The Blackhawk was a great idea and worked very well. The problem was not the drive but the boats. Surface drives don't just bolt on and work on every hull. You essentially loose all ability to trim. For this reason you need to have a boat that creates it's own bow lift. This can be done with air entrapment, rocker hulls etc... Bolting a Blackhawk, or any surface drive, onto a convential v hull needs to be thought out real well. It can be done but if you don't know what you are doing it might not work. So back to Blackhawks. It was a true surface drive as both props were designed to be 1/2 in and 1/2 ( more or less) out of the water. To really gain the full potential of a surface drive you really need to build the hull around the drive and that was not something the market was prepared to do. Not only would most hulls need a complete redesign but honestly the drive was still to long. Mercruiser required the drive to be mounted higher then the stock bravo and despite the diminutive length of the Blackhawk still sat too low in the water or the engine was so high that CG was all messed up and hatches had to be domed bubbled and butchered.
It is a real tough propostition you got there...
Want to talk about a duo prop arneson...that would get my attention....
Chris
The Blackhawk was a great idea and worked very well. The problem was not the drive but the boats. Surface drives don't just bolt on and work on every hull. You essentially loose all ability to trim. For this reason you need to have a boat that creates it's own bow lift. This can be done with air entrapment, rocker hulls etc... Bolting a Blackhawk, or any surface drive, onto a convential v hull needs to be thought out real well. It can be done but if you don't know what you are doing it might not work. So back to Blackhawks. It was a true surface drive as both props were designed to be 1/2 in and 1/2 ( more or less) out of the water. To really gain the full potential of a surface drive you really need to build the hull around the drive and that was not something the market was prepared to do. Not only would most hulls need a complete redesign but honestly the drive was still to long. Mercruiser required the drive to be mounted higher then the stock bravo and despite the diminutive length of the Blackhawk still sat too low in the water or the engine was so high that CG was all messed up and hatches had to be domed bubbled and butchered.
It is a real tough propostition you got there...
Want to talk about a duo prop arneson...that would get my attention....
Chris
04-17-2002, 11:44 PM
#6
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Thats an interesting point- I assume a surface drive has to be longer to get 'hard' enough water?
Any idea how mach farther back??
Note: I am talking about something that would be about as heavy as an alpha - lighter than a bravo, although you could prolly add lead to it if you really want hehe...
To address a few other points you raised:
1) If your gimbal can handle your IO, a suface drive should be easier on it because of the lost 'bow lift' type of force
HOWEVER I could see having trouble with steering and maybe trim because of the longer 'lever arm' in those directions.
2) On my boat the horizontal pivots of the gimbal are ~15" above the bottom of the hull, and about 3" above the on-plane water line.
To me that would indicate a 4" or so drop would be ideal (if you want neutral trim to have the prop 1/2 in and 1/2 out) right?
Also, my boat has plenty of bow lift, but its light and stern-heavy...
Thanks for the info, I really do appreciate it
--Adam
Any idea how mach farther back??
Note: I am talking about something that would be about as heavy as an alpha - lighter than a bravo, although you could prolly add lead to it if you really want hehe...
To address a few other points you raised:
1) If your gimbal can handle your IO, a suface drive should be easier on it because of the lost 'bow lift' type of force
HOWEVER I could see having trouble with steering and maybe trim because of the longer 'lever arm' in those directions.
2) On my boat the horizontal pivots of the gimbal are ~15" above the bottom of the hull, and about 3" above the on-plane water line.
To me that would indicate a 4" or so drop would be ideal (if you want neutral trim to have the prop 1/2 in and 1/2 out) right?
Also, my boat has plenty of bow lift, but its light and stern-heavy...
Thanks for the info, I really do appreciate it
--Adam
04-18-2002, 12:20 AM
#7
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No problem I enjoy these threads.
First of all what in the world do you have in mind that will be lighter then a Bravo. I think you underestimate the size this thing has to be. And we still are discounting the whole shifting part. At some point that will need to be addressed and that is going to add some major weigth any way I can figure.
I don't see any possible way this is going to be lighter then a Bravo or even a TRS. There really is no rule of thumb about how far back they have to be. The farther the better. I really would not imagine anything less then 2 feet working well. My arneson is 39 inches and I have it mounted on a 24 inch set back box. We are talking 5 feet!!! The blackhawk worked cause it was duo prop.
In terms of gimble strength don't discount the amount of load this thing will put in the gimble. Aside from the 3 foot long lever arm keep in mind the surface drives put wild vibrations through the whole driveline. Due to the shear size ( length and weight) a surface drive WILL put a LOT more load on your gimble. Also Don't forget you are going to need to torsionally control this thing from rotating. That adds even more stress. We are talking about a major stress strain analaysis here before we even get close.
Also I think you have the drop wrong. You are going to need the prop a couple inches above the absolute bottom of the keel. So we are talking more like a 12 inch drop!!! Not easy.
Basically what it comes down to, IMHO, is that unless you are a major company ( Merc) willing to completely retool for something like this there is absolutely no way to do this cheaper, easier or better the going right to an Arneson. Sorry to sound so bleak. I have thought this through and if I thought it could be done within reason I would have
Chris
First of all what in the world do you have in mind that will be lighter then a Bravo. I think you underestimate the size this thing has to be. And we still are discounting the whole shifting part. At some point that will need to be addressed and that is going to add some major weigth any way I can figure.
I don't see any possible way this is going to be lighter then a Bravo or even a TRS. There really is no rule of thumb about how far back they have to be. The farther the better. I really would not imagine anything less then 2 feet working well. My arneson is 39 inches and I have it mounted on a 24 inch set back box. We are talking 5 feet!!! The blackhawk worked cause it was duo prop.
In terms of gimble strength don't discount the amount of load this thing will put in the gimble. Aside from the 3 foot long lever arm keep in mind the surface drives put wild vibrations through the whole driveline. Due to the shear size ( length and weight) a surface drive WILL put a LOT more load on your gimble. Also Don't forget you are going to need to torsionally control this thing from rotating. That adds even more stress. We are talking about a major stress strain analaysis here before we even get close.
Also I think you have the drop wrong. You are going to need the prop a couple inches above the absolute bottom of the keel. So we are talking more like a 12 inch drop!!! Not easy.
Basically what it comes down to, IMHO, is that unless you are a major company ( Merc) willing to completely retool for something like this there is absolutely no way to do this cheaper, easier or better the going right to an Arneson. Sorry to sound so bleak. I have thought this through and if I thought it could be done within reason I would have
Chris
04-18-2002, 12:46 AM
#10
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Ok... First couple of philosophical differences... This is really meant as a replacement for a good alpha or stock bravo drive. Its for the person that cannot possibly affoard to put $8-20k into a drive.
Hehe, well the length of the drive is the real issue... I could stuff what Im thinking of into about 16" behind the pivot in the gimbal, if you don't need the drop.
The rotational load on the gimbal I hadn't considered, is this because you dont have the 'keel' like effect of the outdrive?
As for weight- well it will weigh as much as a bravo with the drop and extra 2' of extension I would think.
The drop IS something I don't have an answer for. I could get to 4 or even 8" easily, but 12", thats gunna take some gear speed consideration... I don't think reasoably priced gears like 6000fps kinda speeds...
I also had not really thought about the vibration on the gimbal- see I know I was missing stuff
Arg... Would there be much market for an outdrive with integral 10" sternjack type feature? hehe
It really isnt just a matter of better than the other companies- its that they have HUGE margins because people have to pay the money. That is ok for the people who can affoard it, but there are plenty of people that really could use the product and could affoard to pay a more realistic price... But obviously not enough to shift the economy of scale in that direction.
(BTW the vibrations would be 3/4/5x the prop speed, or so, right?)
--Adam
Hehe, well the length of the drive is the real issue... I could stuff what Im thinking of into about 16" behind the pivot in the gimbal, if you don't need the drop.
The rotational load on the gimbal I hadn't considered, is this because you dont have the 'keel' like effect of the outdrive?
As for weight- well it will weigh as much as a bravo with the drop and extra 2' of extension I would think.
The drop IS something I don't have an answer for. I could get to 4 or even 8" easily, but 12", thats gunna take some gear speed consideration... I don't think reasoably priced gears like 6000fps kinda speeds...
I also had not really thought about the vibration on the gimbal- see I know I was missing stuff
Arg... Would there be much market for an outdrive with integral 10" sternjack type feature? hehe
It really isnt just a matter of better than the other companies- its that they have HUGE margins because people have to pay the money. That is ok for the people who can affoard it, but there are plenty of people that really could use the product and could affoard to pay a more realistic price... But obviously not enough to shift the economy of scale in that direction.
(BTW the vibrations would be 3/4/5x the prop speed, or so, right?)
--Adam
