gearboxes and potential

Advice on automatic transmission

Like Bobber I'm interested to learn whether an automatic car gearbox can be used on a recreational small boat. For sound and fun reasons I would like to use an american V8 diesel and smoke my friends. I will not race it so I'm just interested whether it works or not. Is it possible for example to put it in reverse while having forward speed?

Thanks in advance

 

The instalation will need a thrust bearing as the auto tranny was not designed to push on, as a boat shaft does.

IT will be one HECK of a bearing to accept the loads from shifting into reverse at speed!

AT low speeds there should not be a problem (docking ) BUT AT 40+ WOW!

FAST FRED

 

Here we go again? Gonzo had the idea of a seperate thread on conversions. I am with him on it. Automatic 2 speed transmissions were completly developed by Mercruiser just for stern drives to give much better acceleration. They worked perfectly. This was just 3 years ago. They dropped it like a hot potato because NO boat manufacturer would be first to buy and have to raise his prices. However- drag boats do use a very close ratio 2 speed to get a better jump off the line. I wanted to use the Nissan 5 speed auto. It turns out that HI gear and the one before are the only two that would be close enough. That is what the prop engineers at Michigan Wheel and I came up with. I can send a scan to this web site of the emails in writing I have. The limiting factor is at max engine speed and a given gear ratio only 1 prop is perfect. Logic now tells me that all those lower ratios will multiply torque so much in each gear that ramming the throttle home from a dead stop would sound like one quick high scream as the trans shifts as fast as it revs up in each gear. Remember the prop can't change size to use all the torque of each gear. If we put a controllable pitch prop on the shaft and floor it- it would then be able to develope about 385 ft lbs X 1st gear of 3.83 = 1474 ft lbs X torque converter ratio of ? 2 ? = 2949 ft lbs twisting the prop shaft at stall speed of transmission. It could snap a persons neck with ease. Here is where it gets scary if the continously adjustable prop is used. The same engine and prop geared at 1 to 1 using a Michigan 13 X 10 X 3 blade w/heavy cup will develope 1500 pounds of foward thrust. If 380# gives 1500# of thrust. What the devil will 2949# give in foward thrust. I am wise enough not to get in a boat like that.

 

As Richard says, marine automatic transmissions for racing have very close ratios; about 25% difference. Automotive transmissions are about 90% difference. They are designed to work with a torque converter that is basically a propeller in a container ( the torque converter's shell). If you use it in a boat it will have the torque converter and the propeller which is another torque converter. It will loose a lot of HP through slip. A variable/controllable pitch propeller is the best solution. Cargo ships and tugs have used them for decades.

 

Gearboxes

Why aren't you using a Variomatic (DAF)? No clutch, no gears, always optimal torque- it is used in gasturbines (20.000 hp).

Cheers :idea:

 

I was reading about a guy who had a banca built in the philippines,they used a toyota motor n trans.look up banca on the living or life in the philippines yahoo group.

 

Toyota makes a fully MARINEIZED version of the Lexus V8. There is more to motor boating than excluding Asia. They have done very well without USA and Europe. I know that smarts. But that is why big boats are built there, and little ones.

 

Thanks to Bobber

Im interested in Using a Mercedes 5 cylinder diesel in a Marine application, on the cheap, this topic has been extremely informative to me and I have learned alot, Thanks to everyone who has contributed ive copied many of your posts and will ponder on this infomation later,Excellent Thanks, Listinwickedbad

 

For those who would prefer Diesel truck engines to power your bpst, here are some common box ratios: from 15 speed road trucks , likely to be found near new and CHEAP at your local wreckers.

RT-14195
RTO-14715, RTO-15715
RTO-14915, RTO-16915
Gear Ratios
RT RTO
Gear Ratio Ratio
10th 1.00 0.79
9th 1.27 1.00
8th 1.35 1.30
7th 2.14 1.68
6th 2.79 2.19
5th 3.57 2.81
4th 4.54 3.57
3rd 5.90 4.63
2nd 7.63 6.00
1st 9.96 7.83
5th deep 6.07 4.77
4th deep 7.73 6.07
3rd deep 10.03 7.88
2nd deep 12.96 10.20
1st deep 16.94 13.31


Models
RT-14715, RT15715
Gear Ratios
RT
Gear Ratio
10th 1.00
9th 1.27
8th 1.65
7th 2.14
6th 2.79
5th 3.57
4th 4.54
3rd 5.90
2nd 7.63
1st 9.96
5th deep 5.52
4th deep 7.02
3rd deep 9.11
2nd deep 11.80
1st deep 15.40


FAST FRED