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Old 03-30-2023, 05:36 PM   #1
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Tolly 44CMY diesel transmission reduction ratio

Hi fellow Tolly fans,
I recently purchased an amazingly clean 1988 44 cmy with tired Crusader 7.4
350hp engines. I will be biting the big bullet and repowering with 370HP 6BTA Cummins engines and ZF220A transmissions. Does anybody know the factory reduction ratio for the diesel factory installation, and the prop size and pitch for them? That will give my yard a starting point, and we can get transmissions of comparable ratios ordered. Thanks, I'm in the Mid Atlantic area if anyone wants to touch base and maybe get together. Thanks
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Old 03-30-2023, 06:30 PM   #2
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Welcome to the forum and Congratulations on your purchase. Sorry I do not know the reduction ratio you are needing, hopefully someone will have it for you.
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Old 03-30-2023, 07:40 PM   #3
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If you want a starting point, goto vicprop.com and use their calculator
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Old 03-30-2023, 07:50 PM   #4
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I wouldn't worry too much about what they necessarily did from the factory, especially as your 6BTAs rev higher than the factory 3208s. I'd try to come up with an idea of how fast the boat should run, and then measure for the maximum prop diameter you can fit. Knowing those, you and the yard should be able to calculate a good gear ratio and prop combination.

Knowing that the 6BTA 370 is rated at 3000 RPM, you'd want to target ~3100 for prop selection. With a 1.75:1 ratio transmission and assuming a 24 kt top speed, a calculator comes up with a 24x21 as the suggested 3 blade prop or a 22x22 4 blade. With a 2:1 transmission, it recommends a 26x23 3 blade or a 24x24 4 blade. I expect 24" is probably in the ballpark for diameter, so that should give you a starting point to figure it out once you measure and confirm.
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Old 03-30-2023, 07:54 PM   #5
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Boatdiesel.com has several calculators that will help you.
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Old 03-30-2023, 08:09 PM   #6
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Welcome aboard. Congrats on your new boat. Please start a thread on the repower project and take lots of photos, we love photos.
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Old 03-30-2023, 08:57 PM   #7
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Quote:
Originally Posted by rslifkin View Post
I wouldn't worry too much about what they necessarily did from the factory, especially as your 6BTAs rev higher than the factory 3208s. I'd try to come up with an idea of how fast the boat should run, and then measure for the maximum prop diameter you can fit. Knowing those, you and the yard should be able to calculate a good gear ratio and prop combination.

Knowing that the 6BTA 370 is rated at 3000 RPM, you'd want to target ~3100 for prop selection. With a 1.75:1 ratio transmission and assuming a 24 kt top speed, a calculator comes up with a 24x21 as the suggested 3 blade prop or a 22x22 4 blade. With a 2:1 transmission, it recommends a 26x23 3 blade or a 24x24 4 blade. I expect 24" is probably in the ballpark for diameter, so that should give you a starting point to figure it out once you measure and confirm.


Itís a bit more complicated as the OP states he has Crusader gas engines which will run up to 4000+ rpm WOT. Trans ratios will be much different and possibly prop diameter/pitch.
Prop calculators should be able to get to the ball park, but input from a diesel Tolly owner would be ideal

James
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Old 03-31-2023, 03:36 AM   #8
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Originally Posted by MacPhid View Post
Itís a bit more complicated as the OP states he has Crusader gas engines which will run up to 4000+ rpm WOT. Trans ratios will be much different and possibly prop diameter/pitch.
Prop calculators should be able to get to the ball park, but input from a diesel Tolly owner would be ideal

James
It sounds like he's getting new transmissions with the new engines, so what he has now shouldn't be a concern.
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Old 03-31-2023, 06:31 AM   #9
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It was mentioned that the new 6BT engines would rev higher than CAT 3208 engines but his current setup is 7.4l gas revving higher than the Cummins. Knowing what current owners of that model boat with diesels are running for gears and props would, as the OP asked, put the yard in the ballpark for ratios.

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Old 03-31-2023, 08:13 AM   #10
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Does a 1988 boat warrant new diesels? Your cost will be well over $150,000. Is the boat worth it?

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Old 03-31-2023, 09:00 AM   #11
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Originally Posted by rslifkin View Post
I wouldn't worry too much about what they necessarily did from the factory, especially as your 6BTAs rev higher than the factory 3208s. I'd try to come up with an idea of how fast the boat should run, and then measure for the maximum prop diameter you can fit. Knowing those, you and the yard should be able to calculate a good gear ratio and prop combination.

Knowing that the 6BTA 370 is rated at 3000 RPM, you'd want to target ~3100 for prop selection. With a 1.75:1 ratio transmission and assuming a 24 kt top speed, a calculator comes up with a 24x21 as the suggested 3 blade prop or a 22x22 4 blade. With a 2:1 transmission, it recommends a 26x23 3 blade or a 24x24 4 blade. I expect 24" is probably in the ballpark for diameter, so that should give you a starting point to figure it out once you measure and confirm.
The prop size and configuration makes a huge impact and you really need to look at the geometry of your running gear before committing to any big plans. Generally, diesel driven props spin a lower speeds and are larger in diameter, they require larger diameter shafts to withstand the higher torque of diesel drivetrains. You should not assume that your current running gear shaft angle, length and current prop position will work with your new drivetrain.

Your best bet would be to find a diesel powered Tolly like yours and go take a bunch of measurements. That may require a trip to the west coast where Tolly's are more prevalent, or to hire a local mechanic to do it for you.

You may be able to reduce much of the cost and expense of this endeavor by going with the 210HP configuration of the B series and retaining your current shafts, struts, and approximate prop diameter. You would limit your speed obviously but it may be worth the tradeoff.
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Old 03-31-2023, 09:31 AM   #12
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As GD suggests, query the West Coast. Some years ago I spent some time with the owner of a T45 who did the same as you desire with a fresh install of 6BTs. He was part of the predicted log log group out of Seattle.

The Tolly Forum should be able to assist too. As OEM, the 45s came with Crusader Gas, DD 8.2 and Cat 3308s. There may indeed be a 6BT OEM out there. Iíve run the T48 with 6BTs, a great combination.

Youíre on the right track provided your installer is capable. Iíd view the yardís job to be fully capable of figuring out the drive train. If they canít, maybe a concern as to their abilities.

I know several well experienced yards in the PNW whoíd have no trouble figuring the install out. Maybe ask Zimmerman on the East Coast. Ask Steve D on this site whoíd he recommend.

Good luck and I trust youíve budgeted a complete ER makeover as part of this deal.
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Old 03-31-2023, 10:04 AM   #13
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Thanks to all for the input. Just to add to my situation, I know the repower is a huge financial step. My plan is to do the great loop, now that i'm retired. My wife likes the design of the aft cockpit, and I am really partial to Tollycraft design and build quality. This particular boat was shed kept and very well maintained. Any factory Tolly diesel 44/45 would still have 28-35 year old diesels, this way I at least have warranty . Zimmerman is doing the job, and they have the experience and reputation. One thing about Tollycraft, the shafts struts and exhaust thru hulls are the same whether gas or diesel. Big savings. Just looking at the dollar side, for the price of the boat plus the repower and complete engine room makeover and new fuel tanks, the total is not that far over what like year models with 30+ year old engines are going for. I might be crazy, but what the heck, can't take it with you.
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Old 03-31-2023, 10:43 AM   #14
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Youíve got it figured out. While youíre at it double check with Tony Athens regarding the raw water pumps. Some of the 6BTs come with less than adequate Sherwoods.
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Old 04-14-2023, 05:55 PM   #15
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For what itís worth, I have a 1986 Tolly 44í CPMY.

Has twin Cat 3208 NAs - 210hp
Reverse gears are Twin Disc MG502. 2:1 gear ratio
Canít find the prop info at the moment.

Tollyforum used to be an incredible resource until a few years ago when something happened with their server and decades of useful information was lost. Havenít checked back recently.

Youíll love that boat. Happy to help with things you may run into on it. Iíve been crawling around replacing almost everything but the engines on mine for almost 10 years.
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Old 04-15-2023, 09:54 AM   #16
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Same boat...

I have a Tolly 40 Sundeck with those exact engines and transmissions as you describe.

It has 2 to 1 reduction in the ZF 220 and I am running 4 blade 24 by 24 props.

The boat runs very comfortably at 18 to 20 knts @ 2300 rpm. Tops out around 25 @ 3050 rpm.

We run slow at 8.5 and 1200 rpm.

I really like the installation, it gives lots of room to maintain the engines and Onan genset. Gives the old boat a new life!

Cheers. Gary
MV Sunlady
Sidney BC
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Old 04-17-2023, 06:16 AM   #17
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My 1992 44 came with 375 HP 3208TAs turning 26x26 three blade wheels through a 2:1 reduction gear. I have no reason to believe that this was not the factory setup.
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Old 05-03-2023, 11:29 AM   #18
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Reduction ratio

Many thanks to all for your input. Special thanks to ORIF, islandmech, and mischief managed, for their technical specs and data. Will keep posting as this adventure continues!!
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