Searay 180 Outboard shaft length

Ricardo Oberpaur

New Member
Feb 5, 2020
8
Boat Info
1992 Searay 180 BR/OB and 1993 Searay 180BR
Engines
2.5L 175hp Mariner and 4.3L v6 Mercruiser
Hello,

I am new here, I will probably ask too many questions for some time, please bear with me :)

I am the happy owner of a 1993 Searay 180 BR still in perfect condition, and have now added a 1992 180 BR/OB to the list. It needs some love, but it will be a beautiful boat once finished. Upholstery, guard rail, emblems, some gelcoat repairs and it will be almost perfect.

One of the things I need to do is change the motor. The 175hp carbed v6 is very thirsty. I have another boat that will welcome this engine :)

Do you know what shaft length the 180 OB motor should be? I have conflicting information... Some tell me 20", some others 25".

Thanks!!
 
Is it a 1982 or 1992 180 that you recently picked up? Your profile says 1982, but your question asks about a 1992? Either way that boat must fly with a 175OB. Good luck with her and post some pics of the before and after.
 
Is it a 1982 or 1992 180 that you recently picked up? Your profile says 1982, but your question asks about a 1992? Either way that boat must fly with a 175OB. Good luck with her and post some pics of the before and after.
You are right!.... It's a 1992 boat. I'll correct that.
She runs 56 mph with a 21" black max alum prop. The I/O does 49 with a Mach 4 blade SS prop.
 
According to the 1993 propeller chart the 180 BR has a 20 inch shaft ( https://www.searay.com/us/en/owners.html ). The 1982 and 1992 propeller charts don't give shaft length, but its probably the same as 1993.

The chart also indicates that 135 hp was the largest engine offered. 175 hp is probably too much engine for that boat.
 
According to the 1993 propeller chart the 180 BR has a 20 inch shaft ( https://www.searay.com/us/en/owners.html ). The 1982 and 1992 propeller charts don't give shaft length, but its probably the same as 1993.

The chart also indicates that 135 hp was the largest engine offered. 175 hp is probably too much engine for that boat.

Thanks for the info!
Strange that the I/O can run a heavy 175hp piece of iron, and the O/B only a 135. That said, I have seen at least two other boats like mine also running a 175 v6. On mine after 28 years the transom looks pristine, it handles well at WOT..... I have to admit I am looking at a 250hp Yamaha for this boat:)
Having driven a 1982 Glastron Carlson C-500 with 175hp, it can't be worse :p
 
Here's the I/O.
 

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This is making me miss my 95 180BR. It only had a 90hp merc hanging off the back and I do remember the specification tag by the throttle saying 125HP was the max motor size. We hit 42mph gps speed one time with the wind to our back and glass surface. I thought a couple times about going up to a 125. But, sold the boat after we got the Dancer.
 
I never understood how the max hp for a Hull is defined. The BR's max is 125hp, the Closed Bow's max 175hp. Is there any structural difference in the Hull to justify this?.... Don't think so.
 
There shouldn't be any difference between the HP rating of a BR vs CB. What are you looking at that shows that? My info shows them being rated the same, which is what I've always seen over the years.

Concerning the OB Max HP rating vs an I/O Max HP rating... I'd only be guessing, but I think it would have to do with where the weight is being placed on the boat. With an I/O, the weight is distributed over a MUCH larger area of the boat and directly onto the stringers. Plus, the outdrive is sandwiching the transom (1) over a larger area than an OB and (2) lower on the transom. An OB is placing all of it's weight and torque at the top of the transom (think "leverage").

Something else to keep in mind... back in the day, an I/O's advertised HP was measured at the crank, as opposed to an OB where it is measured at the prop. Nowadays, I/O's advertise only the propshaft HP. So, that 175HP was really only something like 150HP/155HP (apples to apples).

That stuff aside, nice looking boat!
 
There shouldn't be any difference between the HP rating of a BR vs CB. What are you looking at that shows that? My info shows them being rated the same, which is what I've always seen over the years.

Concerning the OB Max HP rating vs an I/O Max HP rating... I'd only be guessing, but I think it would have to do with where the weight is being placed on the boat. With an I/O, the weight is distributed over a MUCH larger area of the boat and directly onto the stringers. Plus, the outdrive is sandwiching the transom (1) over a larger area than an OB and (2) lower on the transom. An OB is placing all of it's weight and torque at the top of the transom (think "leverage").

Something else to keep in mind... back in the day, an I/O's advertised HP was measured at the crank, as opposed to an OB where it is measured at the prop. Nowadays, I/O's advertise only the propshaft HP. So, that 175HP was really only something like 150HP/155HP (apples to apples).

That stuff aside, nice looking boat!

You are right, I misread the document (prop chart mentioned in a previous post by Chip).
Thanks also for the thoughts about I/O vs O/B.
I will post pictures of the O/B once it's looking as it should :)
 
There should be a maximum HP rating on the capacity plate by the throttle. The maximum HP for my 1993 Sea Ray 200 Overnighter OB is 150 hp.
 
I'll add one tidbit of unsolicited advice, concerning that "thirsty" 175HP OB. Have you checked the prices of OB's lately? You're looking at roughly $15K for a 150HP Merc with controls. That buys an AWFUL lot of gas. Plus, putting a $15K engine on a '93 boat doesn't mean the boat is immediately worth $15K more... you'd probably lose $7K in value right away. I'm just spitballin' here, but you get the idea... or at least my opinion, anyways - run the snot out of that sweet, oil burnin', 175HP and don't look back!
 
I'll add one tidbit of unsolicited advice, concerning that "thirsty" 175HP OB. Have you checked the prices of OB's lately? You're looking at roughly $15K for a 150HP Merc with controls. That buys an AWFUL lot of gas. Plus, putting a $15K engine on a '93 boat doesn't mean the boat is immediately worth $15K more... you'd probably lose $7K in value right away. I'm just spitballin' here, but you get the idea... or at least my opinion, anyways - run the snot out of that sweet, oil burnin', 175HP and don't look back!

Fully agree with you. I love the torque and instant power my motor has , but on top of being thirsty, it's a @&!# to start the engine. My significant other does not use the boat just because the probability to get it to run without flooding it is close to zero.

IF I make the jump, it will be another two stroke, but fuel injected.
 
Strange that the I/O can run a heavy 175hp piece of iron, and the O/B only a 135.
Horsepower for I/Os and OBs are determined in different ways. It does have a lot to do with weight distribution but that is not the major factor. The HP for monohull O/B boats under 20 feet in length is determined by a formula that is in the Federal Regulations. It is based on centerline length, maximum transom width, transom height and whether or not the boat has remote steering. These formulas are based on research done back in the 60's and 70's on maneuverability. Essentially, the boats were run through a specific test course the tested their ability to make sharp turns at full speed without losing it.

I/Os and IBs on the other hand are determined primarily by weight of the engine, torque, formulas for determining HP based on resistance and hull shape and so on. HP for I/Os and IB is not regulated by the Coast Guard. OBs are. So essentially it's up to the boat manufacturer to determine what I/O or IB HP they need.

But to answer your first question, probably a 20" shaft. But to be sure measure the distance from the transom cutout where the engine is mounted, down to the bottom of the transom. 19 or more is consider 20, and if its much more than 20 get a 25" long shaft. You want the cavitation plate on the lower unit to be very close to the bottom of the transom. Slightly below is better than being higher than the bottom of the transom. This allows the prop to run in a clean water flow.
 
Hello,

I am new here, I will probably ask too many questions for some time, please bear with me :)

I am the happy owner of a 1993 Searay 180 BR still in perfect condition, and have now added a 1992 180 BR/OB to the list. It needs some love, but it will be a beautiful boat once finished. Upholstery, guard rail, emblems, some gelcoat repairs and it will be almost perfect.

One of the things I need to do is change the motor. The 175hp carbed v6 is very thirsty. I have another boat that will welcome this engine :)

Do you know what shaft length the 180 OB motor should be? I have conflicting information... Some tell me 20", some others 25".

Thanks!!
Use a tape measure to measure the transom height. That way there can be no mistake.
 

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