Start to Finish: Building Our 50' Skater
10-31-2017, 04:40 PM
#1321
Registered
Lets hope it doesn't look like this 1300hp Cummins after six 1/4 mile runs.
Watching this I didn't realize the Cummins doesn't have cross bolted mains, even a mains cap girdle will struggle to hold this together.
https://www.youtube.com/watch?v=60J1155e3h0
Watching this I didn't realize the Cummins doesn't have cross bolted mains, even a mains cap girdle will struggle to hold this together.
https://www.youtube.com/watch?v=60J1155e3h0
This has been an OSO issue for a little while now. Doh !
10-31-2017, 04:52 PM
#1323
Registered
I could not see the link until SB post, using Explorer 11
10-31-2017, 06:21 PM
#1324
Registered
Well, we have a few problems..
We thought the number 8's were going to have a .91 overdrive gear ratio. The day before we ran the boat I checked the ratio and it was 1.1 That is basically 20% less MPH then we thought it would have been able to run. We already were counting on running 40-42 pitch props so you cannot really go any higher in pitch and we would have to do completely different engines to be able to run them at 20% higher rpm and would loose efficiency. So now we have a dilemma, do we try to modify the #8's and have gears made that would be bigger then the outside of the case to where we machine a hole in the side of the case and weld a pocket over it. Or do we design and build overdrive gear boxes and put them possibly between the bell housing and transmission. Which may involve moving engines again, mounts, exhaust, ect.?
There is good and bad about each. By doing the overdrive gear box the good would be we can get more overdrive then we originally were going to have and be able to get more efficient props, be able to run at a lower rpm for efficiency, and not mess with the #8 gears/setup. It would also be better for everything behind it, like the transmission, drive shaft,out drive, prop, ect. by overdriving the output it would lower the torque all those parts see.
The bad about doing the gear box is time and money to design, build, and install it. Plus it will add a few hundred pounds to the boat and be something else that draws power and could break. It will also lead to doing a lot of re-rigging of the engines, mounts ect.
The good about changing the outdrive gears are there is no added weight to the boat, no re-rigging of the engines, possibly quicker and cheaper to make.
And the bad about changing the gears in the outdrive is that it would be better to do it in the lower gears, but they are the weak link because of there small size and I would need them to get smaller. Or cut a hole in the side of the case and make a bump that sticks out each side. The Gears in the lower are forged gears which are stronger then cut gears so we would either have to make a forging for them which would be expensive or risk them not being as strong. And there is not enough room in the upper to get that much overdrive. The setup/backlash in the lower is very critical to them living and it would basically be unchartered territory so we would have to chance ruining some outdrives to find out.
I think the less risky thing is to make an overdrive box that goes in-between the trans and bell housing. I basically need to make the overdrive gear box look like the transmission on the front side to go into my bellhousing, and the other side will need to look like the bell housing where the transmission shaft would stick into the overdrive box just like it does into the bellhousing/spring damper.
At the point the night before I ran it when I figured out that the gear ratio was wrong I almost quit working on it because this is a major problem that basically ruined everything I had worked on for months. Had I known we would not have had the overdrive ratio I would probably not have taken the arnesons off and would have tried to deal with the issues we were having with them. But I never give up so here I am trying to design and build more parts for the boat to try to get it to run.
.
We thought the number 8's were going to have a .91 overdrive gear ratio. The day before we ran the boat I checked the ratio and it was 1.1 That is basically 20% less MPH then we thought it would have been able to run. We already were counting on running 40-42 pitch props so you cannot really go any higher in pitch and we would have to do completely different engines to be able to run them at 20% higher rpm and would loose efficiency. So now we have a dilemma, do we try to modify the #8's and have gears made that would be bigger then the outside of the case to where we machine a hole in the side of the case and weld a pocket over it. Or do we design and build overdrive gear boxes and put them possibly between the bell housing and transmission. Which may involve moving engines again, mounts, exhaust, ect.?
There is good and bad about each. By doing the overdrive gear box the good would be we can get more overdrive then we originally were going to have and be able to get more efficient props, be able to run at a lower rpm for efficiency, and not mess with the #8 gears/setup. It would also be better for everything behind it, like the transmission, drive shaft,out drive, prop, ect. by overdriving the output it would lower the torque all those parts see.
The bad about doing the gear box is time and money to design, build, and install it. Plus it will add a few hundred pounds to the boat and be something else that draws power and could break. It will also lead to doing a lot of re-rigging of the engines, mounts ect.
The good about changing the outdrive gears are there is no added weight to the boat, no re-rigging of the engines, possibly quicker and cheaper to make.
And the bad about changing the gears in the outdrive is that it would be better to do it in the lower gears, but they are the weak link because of there small size and I would need them to get smaller. Or cut a hole in the side of the case and make a bump that sticks out each side. The Gears in the lower are forged gears which are stronger then cut gears so we would either have to make a forging for them which would be expensive or risk them not being as strong. And there is not enough room in the upper to get that much overdrive. The setup/backlash in the lower is very critical to them living and it would basically be unchartered territory so we would have to chance ruining some outdrives to find out.
I think the less risky thing is to make an overdrive box that goes in-between the trans and bell housing. I basically need to make the overdrive gear box look like the transmission on the front side to go into my bellhousing, and the other side will need to look like the bell housing where the transmission shaft would stick into the overdrive box just like it does into the bellhousing/spring damper.
At the point the night before I ran it when I figured out that the gear ratio was wrong I almost quit working on it because this is a major problem that basically ruined everything I had worked on for months. Had I known we would not have had the overdrive ratio I would probably not have taken the arnesons off and would have tried to deal with the issues we were having with them. But I never give up so here I am trying to design and build more parts for the boat to try to get it to run.
.
Last edited by BigSilverCat; 10-31-2017 at 06:48 PM.
10-31-2017, 06:44 PM
#1325
Registered
We have started designing the overdrive gear box. It will be a 3 shaft 4 gear arrangement that will keep the output rotation the same as it was. By doing the three shafts I can keep the output basically inline with where it was. I could make the output directly inline but since it will move the driveshaft flange farther back there will be more angle on the driveshaft so I am going to make it with the output moved over two inches and up one inch so the drive shaft angle will be a little better then it was. The bad part about doing that is I will have to make a left and right version. I will also be able to change each of the gear meshes to different ratio's. We will probably build it with enough room to overdrive or under drive it a lot.
10-31-2017, 07:23 PM
#1327
Registered
We have started designing the overdrive gear box. It will be a 3 shaft 4 gear arrangement that will keep the output rotation the same as it was. By doing the three shafts I can keep the output basically inline with where it was. I could make the output directly inline but since it will move the driveshaft flange farther back there will be more angle on the driveshaft so I am going to make it with the output moved over two inches and up one inch so the drive shaft angle will be a little better then it was. The bad part about doing that is I will have to make a left and right version. I will also be able to change each of the gear meshes to different ratio's. We will probably build it with enough room to overdrive or under drive it a lot.
10-31-2017, 07:52 PM
#1328
Registered
10-31-2017, 08:08 PM
#1329
PF Marine
Platinum Member
That sucks, we've all been there..... Hopefully the rotating assembly is fine and no parts went through the motor.
11-01-2017, 06:21 AM
#1330
Registered
My two cents:
There's a high probability that if you re-engineer the out-drives, they will become a weak link and will most likely fail in the end. Given the value of them, it's way to risky and you'll most likely end up with a very expensive pile of garbage.
Given the choice of the overdrive or the out-drives, I'd highly suggest going with the overdrive units. It will be far more reliable (IMO) and you wont waste an expensive set of drives (even IF those customized drives hold, they'd never have any value to anyone else).
Personally, I'd be rethinking the engine choice. I don't know how long those engines will hold together (I wouldn't bet on too long when pushed hard for extended periods in rough offshore conditions). If you go through all the effort to modify the drive-train to get the desired ratio, you're going to possibly be redoing everything anyway if these engines don't prove to reliable when pushed hard under heavy loads for extended periods.
There's a high probability that if you re-engineer the out-drives, they will become a weak link and will most likely fail in the end. Given the value of them, it's way to risky and you'll most likely end up with a very expensive pile of garbage.
Given the choice of the overdrive or the out-drives, I'd highly suggest going with the overdrive units. It will be far more reliable (IMO) and you wont waste an expensive set of drives (even IF those customized drives hold, they'd never have any value to anyone else).
Personally, I'd be rethinking the engine choice. I don't know how long those engines will hold together (I wouldn't bet on too long when pushed hard for extended periods in rough offshore conditions). If you go through all the effort to modify the drive-train to get the desired ratio, you're going to possibly be redoing everything anyway if these engines don't prove to reliable when pushed hard under heavy loads for extended periods.
