Will my new transmission work?

[Awlwet]

I had to replace a worn out Kanzaki transmission and bought the only one I could find. I was assured it was the same as my bad one, but when it arrived it was a 3.3 to 1 and the bad one is a 2.1 to 1. Can I still use this transmission and what difference will I be looking at. Please help, I need to leave California and get through the Panama Canal. I want to do it without experiencing anymore transmission problems.....

[Sailmonkey]

The new one will still work, however your prop pitch is now wrong.

If your fine with the engine running faster and the boat moving more slowly then carry on.

Do you have a feathering prop that you can change the pitch of?

[Wotname]

It will depend also on how well your existing prop was matched to your old transmission.

[GordMay]

Greetings and welcome aboard the CF, Awlwet.

[coastalexplorer]

IF the original transmission was over stressed & failed because the prop was over pitched. wouldn't the higher ratio tend to fix the problem?

[seabreez]

Originally Posted by Awlwet

I had to replace a worn out Kanzaki transmission and bought the only one I could find. I was assured it was the same as my bad one, but when it arrived it was a 3.3 to 1 and the bad one is a 2.1 to 1. Can I still use this transmission and what difference will I be looking at. Please help, I need to leave California and get through the Panama Canal. I want to do it without experiencing anymore transmission problems.....

If I understand this correctly 3.3 to 1 means the engine turns 3 revolutions for 1 revolution of the propeller and 2.1 to 1 means the engine turns 2.1 revolution for one revolution of the propeller. This means that this 3.3 to one will have more torque and less speed and was designed this way. Now you want to change and go with less torque and more speed. This means that the engine will try to reach a speed that it was not designed for and therefore will labour more and maybe overheat and you may not reach the speed you are comfortable of reaching. The difference bet 3.3 and 2.2 ratio is almost 1/3 difference. If you remain with this transmission you will surely have to change your propeller. Ask a propeller shop about this transition... good luck...

[Uncle Bob]

For a given engine speed the prop will turn slower with the 3 to 1 ratio, meaning the boat will be slower at the given engine speed. If you wish to have similar performance characteristics to the previous transmission then you will need a prop with a different pitch.

[seabreez]

Originally Posted by Uncle Bob

For a given engine speed the prop will turn slower with the 3 to 1 ratio, meaning the boat will be slower at the given engine speed. If you wish to have similar performance characteristics to the previous transmission then you will need a prop with a different pitch.

Be careful here, the boat may not be slower. If the boat was designed to reach hull speed with that particular engine and transmission and you change the transmission (ratio) then change the prop to meet the same speed and torque curve. This is not rocket science but you have to calculate the prop pitch according to engine speed and weight of the vessel

[Sailmonkey]

Originally Posted by coastalexplorer

IF the original transmission was over stressed & failed because the prop was over pitched. wouldn't the higher ratio tend to fix the problem?

Yes, No, Maybe.....depends.

[seabreez]

Originally Posted by coastalexplorer

IF the original transmission was over stressed & failed because the prop was over pitched. wouldn't the higher ratio tend to fix the problem?

If... ? Overstress...? It is hard to investigate wear and stress of a transmission unless you can visualize the gears and clutches and bearings. Making design changes is always a risk followed by more modifications. Modifications have to be studied very very carefully to minimize risk of errors and make sure you have an alternate plan if something goes wrong.

[seabreez]

I forgot to answer your question... yes by increasing the ratio you would be helping the situation. The key thing is not to go too high...

[coastalexplorer]

To..Awlwet

As I already posted the diameter and pitch of the existing propeller is the key factor affecting the answer to your question. If the boat is out of the water? you should be able to clean and read the info off of the propeller?

The very short logical answer to your original question is of course you can install the transmission that you have bought because it is a higher ratio it will put less stress on the engine IF you run it at the same top speed in terms of revolutions per minute.

IF,*BTW... *that is the most important two letter word in the English language*
IF the propeller was matched correctly in the first place the vessel is liable the proceed at a slower speed generally, It just might go against current and steep waves slightly better. especially IF it has three or four blades. but it is reasonable to expect that it will use more fuel for distance traveled.

IF However the previous owner installed a propeller that was a Higher pitch than required, Either because they found one second hand for cheaper and thought it close enough, Or got greedy thinking a bigger bite in the water would give more speed. This could account for the failure of your 2.1 to 1 transmission. IF this is the case the replacement Transmission might tend to fix the problem that you did not know you had and get you where you are going. (which it is liable to do in any case the only question under debate at this point is how efficiently)

That having been said... IF You have the time..Which you say you are pressed for...The real solution is to note the existing propeller specification then open up a propeller calculating programme and run the numbers. 51 % chance you might be pleasantly surprised by the answer.