I know this subject has been pondered before...but with the advanced technology available today why aren't there Multi Speed transmission being utilized in the marine industry ?

It would really allow taking advantage of the torque curves of any engine.

There are 2 Speeds

ok...on a car/truck a multi gear trans is used because your just not leaving a traffic light in 5th gear

On most boats your proped at the final drive ratio to optimize what the boat will pull,,

Say you have a 38 scarab with 800 hp motors that runs 95 at 5800. Now if you are sitting still and mash the sticks to the dash, you are just going to blow the props out instead of comming up on plane. This would be the equivalent of smoking the tires.

So if your car that does 150 in 5th gear can smoke the tires off the line in 5th gear, there really isnt much reason for a transmission is there??

At least thats my take on it...

I believe there is a couple out there, to include a 3 speed. Prop the boat for WOT in first gear at lets say 6000rpm, each gear is a 6% reduction. So, run the boat up to 6000 in first gear, shift to second(6% reduction). Now the rpm drops to 5600 and you can run the boat back to 6000 again. Shift to third, back to 5600 again, put the sticks thru the dash to 6000 one more time. Now her a** is covering some real-estate!!!! This can be done at any rpm to achieve cruise speed/rpm or max speed. We have a set of 3 speeds that are going in a MTI with 1180hp a side, no telling what this boat is going to run, but I can keep all posted if you would like. Prop testing is going to be the next hurdle after install is complete

The one thing that won't happen is ..It will not change top speed on a properly propped(engine turning target rpm at wot) boat...

I don't think that is a accurate statement...As gear changes, so does ratio
Pitch Ratio RPM Speed Slip
41 1.24 6000 165 12% 1st
41 1.18 6000 174 12% 2nd
41 1.12 6000 183 12% Final Drive

I'm not sure I understand the point of the transmission in your application. If the boat has enough power to run 183 mph it will do so with or without the transmission. If you are trying to make it easier to handle around the docks a 2-speed would take care of that. You aren't getting free speed by having more ratios. If it needs all 1180 hp per side to run 165 shifting to a higher gear won't magically make it run faster. Look at any chart in a Car and Driver road test. A lot of cars they test hit top speed in 4th gear where they can reach redline. They may run the same or close in 5th or 6th but never faster.

But hey its not money do it and prove me wrong, I certainly don't have all the answers!

The reason boats don't typically have transmissions is because they need all the power they make at a given RPM to go a certain speed.

it might change the top speed due to the parasitic loss from turning the xtra parts in the multi speed trans.could drop 1 ot 2 mph.

drag boats have used a two speed transmission for years.gear reduction for quicker et.

I think some boats would benefit greatly from 2 speed transmissions. Fact of the matter is they will help the boat accelerate faster which makes it faster a 100mph boat that accelerate like its on fire will always beat up on a 120mph boat that takes miles and miles to reach top speed. What happens if you have a 40+ foot v-hull with big boy props and it takes a mile to plane out? I don't think it's very good on the motor when it's so loaded its pulling 3lbs of boost just to get on plane. With all the fancy fuel injected stuff running around now I think a 2 or 3 speed transmission added into the mix that was electronically controlled can make for a rocket ship. How many guys have a boat that chine walks at certain speeds and it takes the boat some time to get through that 5-10mph worth of chine walk. Just imagine how much better it would be if you could drop down a gear and accelerate through it much faster. If you could you might not even notice the boat chine walks.