Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

[david_tye]

Hello all,

I own an '89 Sunbird with the OMC 3.0 currently running a 13x19 3-blade aluminum prop; top speed: 35mph, WOT rpm: 4200. I'm going to change over to 4-blade props for better performance with a load.

I am thinking about a 17p or 18p for general cruising; i definitely need the better hole shot.

I also want to add around 500-800lbs of ballast in the near future; any suggestions on the prop?

Thanks in advance for any advice,

David

 

[steelespike]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

What size and weight is your Sunbird? In my opinion Your already underperforming for a typical 3.0 and you want to add all that weight.
Is your speed and rpm with a light load?Do you know your gear ratio?(usually on the outdrive) A typical 3.0 would run a 21" at around 40 mph. 4800 rpm.
I don't have the figures for an OMC; at 4200 you may not even be within the wot rpm range.You need to be running a 3 blade17" to get in the range of 4600 that would indicate you need a 16" 4 blade to maintain rpm at your present setup.If your going to add 500-800 I doubt you would be within the wot rpm range.

 

[david_tye]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

What size and weight is your Sunbird? In my opinion Your already underperforming for a typical 3.0 and you want to add all that weight.

19'...i think it's around 2700lbs. I was under the assumption that 35mph was a pretty typical top speed for this size vessel w/ the 3.0

Is your speed and rpm with a light load?Do you know your gear ratio?(usually on the outdrive) A typical 3.0 would run a 21" at around 40 mph. 4800 rpm.

35mph is only with me and a full tank of gas. I don't know the gear ratio. For some reason I thought the recommended WOT rpm for this motor is 4200-4300.

I don't have the figures for an OMC; at 4200 you may not even be within the wot rpm range.You need to be running a 3 blade17" to get in the range of 4600 that would indicate you need a 16" 4 blade to maintain rpm at your present setup.If your going to add 500-800 I doubt you would be within the wot rpm range.

I'm relatively pleased with my 19p 3 blade for cruising...I totally expect to change props when I load up the ballast; therefore, my question is directed more towards my prop selection for that particular situation.

 

[steelespike]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

OK your performance is more in line for a 19 footer. Though they can be as light as about 2200 and as heavy as about 3000,
depending on the model.Unfortunately I don't have the specs for the OMC. I would guess 4600 max rpm. You might try a search.
Perhaps someone will be along with more info.
I would test run it with the ballast to get an accurate indication of the best prop.
A brief search turned up 4200-4600 rpm.
I believe for best control at wake board speed propping for higher rpm at wot will produce better control.
A 17"prop would put you at about 4500 to 4600 and again probably be easier to control at wake board speed with improved hole shot.
Of course after ballast prop size may change.

 

[david_tye]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

OK your performance is more in line for a 19 footer. Though they can be as light as about 2200 and as heavy as about 3000,
depending on the model.Unfortunately I don't have the specs for the OMC. I would guess 4600 max rpm. You might try a search.
Perhaps someone will be along with more info.
I would test run it with the ballast to get an accurate indication of the best prop.
A brief search turned up 4200-4600 rpm.
I believe for best control at wake board speed propping for higher rpm at wot will produce better control.
A 17"prop would put you at about 4500 to 4600 and again probably be easier to control at wake board speed with improved hole shot.
Of course after ballast prop size may change.

I had the boat out yesterday with some "field-expedient" ballast...the 19p 3-blade is definitely not going to cut it. with about 500lbs and a wakeboarder, the boat takes forever to plane off. Cannot plane off at all with the ballast and two inflatables. Top speed with 4 adults and 3 children was 30mph at about 3600 rpm WOT.

I cant find a 16p 4-blade prop...what do you think about a 15p 4-blade?

Thanks

 

[doyall]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

Used to have a similar set up and found after trying numerous props that a 15 x 17 SS was the best all round. Even then I couldn't imagine the frustration trying to do watersports with 500 - 800 pounds of ballast. If you are intent on doing that, better go for a 15 pitch and then it will still be a struggle.

 

[david_tye]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

Used to have a similar set up and found after trying numerous props that a 15 x 17 SS was the best all round. Even then I couldn't imagine the frustration trying to do watersports with 500 - 800 pounds of ballast. If you are intent on doing that, better go for a 15 pitch and then it will still be a struggle.

3-blade or 4-blade?

 

[doyall]

Re: Adding fat-sacs to an '89 Sunbird w/ 3.0 OMC

3-blade or 4-blade?

Three blade.