fujimo42
08-06-2009, 06:55 PM
Have any of you had any experience using a jack plate to install a 25" shaft motor on a 20" transom. Is this common practice or considered a no no? The boat is rated for a 175hp and I'm installing a 150hp.
The Boating Forum - 25" shaft motor on a 20" Transom
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View Full Version : 25" shaft motor on a 20" Transom
CapnDean
08-06-2009, 06:57 PM
it can be done but I'd spend my time hunting a 20". The headache you will have getting it right is gonna cost you the benefit you have with using your 25" shaft.
I am assuming you HAVE a 25" shaft good running 150 already and are trying to use it to save the money you'd spend getting a 20" shaft motor....am I right?
I am assuming you HAVE a 25" shaft good running 150 already and are trying to use it to save the money you'd spend getting a 20" shaft motor....am I right?
fujimo42
08-06-2009, 07:05 PM
it can be done but I'd spend my time hunting a 20". The headache you will have getting it right is gonna cost you the benefit you have with using your 25" shaft.
I am assuming you HAVE a 25" shaft good running 150 already and are trying to use it to save the money you'd spend getting a 20" shaft motor....am I right?
I'm having trouble finding a 20" 150hp w/ out breaking the bank and have located a 25" thats in like new condition that I think is a good deal.
I am assuming you HAVE a 25" shaft good running 150 already and are trying to use it to save the money you'd spend getting a 20" shaft motor....am I right?
I'm having trouble finding a 20" 150hp w/ out breaking the bank and have located a 25" thats in like new condition that I think is a good deal.
BigNiner19
08-06-2009, 09:16 PM
You could get a jackplate
welder
08-06-2009, 09:57 PM
Get a JACK PLATE
commuter boats
08-06-2009, 10:11 PM
To make a recommendation I'd like to know more about your boat, is it a particularly light boat?, how much structure ( tower, cabin) is on the boat. A lot of 150s weigh the same as a 175 and raising the weight of the power head will affect the center of gravity of the boat. For a lot of boats this might not be a concern but for a boat that's already low on stability it could be very noticeable affecting both safety and your ability to enjoy the boat.
fujimo42
08-07-2009, 05:25 AM
To make a recommendation I'd like to know more about your boat, is it a particularly light boat?, how much structure ( tower, cabin) is on the boat. A lot of 150s weigh the same as a 175 and raising the weight of the power head will affect the center of gravity of the boat. For a lot of boats this might not be a concern but for a boat that's already low on stability it could be very noticeable affecting both safety and your ability to enjoy the boat.
It's a 26' Bayliner Deck Boat. Its like a pontoon boat all fiberglass. Very stable boat.
It's a 26' Bayliner Deck Boat. Its like a pontoon boat all fiberglass. Very stable boat.
jvclark
08-07-2009, 05:48 AM
Small world- I just replaced a 175 Merc 20" with a 2007 Suzuki DF150 25" on my 1992 Bayliner Rendevoux 26'.
Initally I had motor on second to bottom hole but water coming in back of boat and lots of spray. Raised to second from top and working well.
Because of motor design I went with four blade prop for low speed lift. Top speed is now about 33 versus 38 with 175.
If you pull tubes and like to cruise the 150 will work quite well, but if you want speed then stay with 175 and three blade.
Bottom line - I think the mounting of a 20" shaft on the Bayliner was a little short and lead to cavitation, while a 25" is a little long, so you will see advantages to both combo's. If your new outboard is two stroke, you might consider starting with the top hole first.
Enjoy
Initally I had motor on second to bottom hole but water coming in back of boat and lots of spray. Raised to second from top and working well.
Because of motor design I went with four blade prop for low speed lift. Top speed is now about 33 versus 38 with 175.
If you pull tubes and like to cruise the 150 will work quite well, but if you want speed then stay with 175 and three blade.
Bottom line - I think the mounting of a 20" shaft on the Bayliner was a little short and lead to cavitation, while a 25" is a little long, so you will see advantages to both combo's. If your new outboard is two stroke, you might consider starting with the top hole first.
Enjoy
fujimo42
08-07-2009, 06:28 AM
Small world- I just replaced a 175 Merc 20" with a 2007 Suzuki DF150 25" on my 1992 Bayliner Rendevoux 26'.
Initally I had motor on second to bottom hole but water coming in back of boat and lots of spray. Raised to second from top and working well.
Because of motor design I went with four blade prop for low speed lift. Top speed is now about 33 versus 38 with 175.
If you pull tubes and like to cruise the 150 will work quite well, but if you want speed then stay with 175 and three blade.
Bottom line - I think the mounting of a 20" shaft on the Bayliner was a little short and lead to cavitation, while a 25" is a little long, so you will see advantages to both combo's. If your new outboard is two stroke, you might consider starting with the top hole first.
Enjoy
JV, Did you use a jack plate or did you mount direct to the transom. If you used a jack plate, which one did you use? Thanks for your input.
Initally I had motor on second to bottom hole but water coming in back of boat and lots of spray. Raised to second from top and working well.
Because of motor design I went with four blade prop for low speed lift. Top speed is now about 33 versus 38 with 175.
If you pull tubes and like to cruise the 150 will work quite well, but if you want speed then stay with 175 and three blade.
Bottom line - I think the mounting of a 20" shaft on the Bayliner was a little short and lead to cavitation, while a 25" is a little long, so you will see advantages to both combo's. If your new outboard is two stroke, you might consider starting with the top hole first.
Enjoy
JV, Did you use a jack plate or did you mount direct to the transom. If you used a jack plate, which one did you use? Thanks for your input.
epanzella
08-07-2009, 06:54 AM
Back in 1986 I bought a 24ft alum pilothouse boat to put my 25 inch rude 150 on. The boat was special order and came thru with a 20 inch transom do to a screwup on the dealer's part. My choices were keep the boat or miss the summer waiting for another boat with 25 inch transom. I got the dealer to buy me a manual jack plate and the boat had excellent performance over the 10 years I owned her. One caveat, however, the manual jack plate did not have enough range to make up the 5 inches without some modifications on my part. This consisted of drilling some more holes in the bracket and adding some gussets to make up for the strength lost due to overextending the unit. All mods were drill and bolt on, no welding.
commuter boats
08-07-2009, 08:55 AM
It's a 26' Bayliner Deck Boat. Its like a pontoon boat all fiberglass. Very stable boat.
That satisfies my concern for stability but raises concerns about the structure, the longer shaft length and jack plate increases the leverage on the transom and that transom was designed with a very sharp pencil ( it was not overbuilt).
You might consider taking the boat to a shop that could evaluate how the transom is holding up and fabricate a bracket that could spread the stresses out and raise the mounting surface.
That satisfies my concern for stability but raises concerns about the structure, the longer shaft length and jack plate increases the leverage on the transom and that transom was designed with a very sharp pencil ( it was not overbuilt).
You might consider taking the boat to a shop that could evaluate how the transom is holding up and fabricate a bracket that could spread the stresses out and raise the mounting surface.