15 Striper, 1989 Mercury 50-HP Three-cylinder

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Author Topic:   15 Striper, 1989 Mercury 50-HP Three-cylinder

FISHNFF posted 08-03-2013 10:52 PM ET (US)
I do not have performance [data] on the [STRIPER 15 powered by a 1989 Mercury 50-HP three-cyliner enginew with] an old four-blade Comprop. What size Stilletto should I get? The 50-HP Mercury is mounted all the way down but is through bolted, top and bottom. The anti-ventilation plate is above bottom of hull about an inch. There is a 3/4-inch space between motor bracket and top of transom. --FISHNFF
Tom W Clark posted 08-03-2013 11:09 PM ET (US)
12" x 11" Stiletto Star 3.5
Best $200 you'll ever spend on that boat.
FISHNFF posted 08-04-2013 12:56 AM ET (US)
Thanks Tom.
I was thinking 13", but the extra cupping on the Stiletto accounts for that.
What RPM's should that be turning?
Would raising it up a set of holes help?
FISHNFF
Tom W Clark posted 08-04-2013 01:15 AM ET (US)
The WOT Operating Range of the 1989 three cylinder Mercury 50 is 5300-5800 RPM.
My recommendation assumes you have a 1.83:1 gear ratio, though it is possible a 1989 Mercury 50 three cylinder has a 1.64:1 gear ratio. We would need to know the serial number to pin that down.
FISHNFF posted 09-30-2013 07:11 PM ET (US)
Ran the 15 today on the Bay.
Hard to start until I remembered what the previous owner said.
"Squeeze bulb. Choke, no throttle."
Waited, did what he said, "rrrrrrrrrrrr...Vrooom!"
Short story.
Prop was an old Comprop 4x10x13.
The boat was a rocket out of the hole. Very little bow rise trimmed in. Almost none!
Trimmed in all the way it hit 5400RPM, trimmed out where the hull came up and "lightened up", it roared to 5800RPM. Further trimming brought RPM's up without blowing out.
The Quicksilver speedo read 34mph when my buddy next to me showed 30 knots on his GPS, so the speedo indicated 37mph is about right.
I am very impressed.
Yes, it's been a while since ive been enveloped in a cloud of blue smoke. Nostalgic.
I was half hoping the motor would crap out, so I would be justified to buy a new 4 stroke.
Now I just want to buy a new prop, and install a BayStar steering system.
Tom, or anyone, would you recommend the same prop given my performance I experienced today?
Oh, the down side. The motor drank fuel. Like almost as much as my Yamaha F115 on my 18.
Oh well.

Mercury 50EPLT
Serial #OC226798

FISHNFF
Tom W Clark posted 10-02-2013 11:43 AM ET (US)

quote:
Quicksilver speedo read 34mph when my buddy next to me showed 30 knots on his GPS, so the speedo indicated 37mph is about right.
That is ambiguous. Did it hit 34 MPH or 37 MPH? 30 knots is 34.5 MPH

quote:
...it roared to 5800RPM. Further trimming brought RPM's up...
So what was the ultimate RPM reached?
FISHNFF posted 10-02-2013 12:21 PM ET (US)
Sorry.
My speedo was reading 34 at 5400 rpmswhile I was pacing my buddy in his 16 Nausset. His GPS was reading 30.0 knots.
During some WOT runs to 5800 rpms, I got the speedo reading 37mph, so I'm guessing it was pretty accurate.
I did raise the motor up one hole to facilitate through bolting the lower mounts.
The older Comprop, dull finish, is a 4x10x13. Great acceleration and surprisingly did not blow out in turns or when mildly trimming out. I ran around SF Bay, with all the ferry boats and tide and general slop, and boat/motor handled it fine.
I am always looking for a bit more performance, and the polished Stainless "Bling".
Thanks,
FISHNFF
Tom W Clark posted 10-02-2013 12:43 PM ET (US)
37 MPH is pretty darn good.
I'm still not clear if you have a 1.64:1 gear ratio or 1.83:1 gear ratio. If the former, your propeller slip is about 5 percent. If the latter, the slip is about 15 percent. I am not familiar enough with Comprops to know which is more typical.
I also do not know if serial number OC226798 is earlier or later than 5579017, which is the motor serial number after which the gear ratio was changed from 1.64:1 to 1.83:1
My suspicion is that you have the 1.83:1 gear ratio and based on that, and your reported top speed, you would do well with a 12" x 12" Stiletto Star.
FISHNFF posted 10-02-2013 01:09 PM ET (US)
12"x12"?
Do you mean 10.5"x12" in a Triad II?

Thanks,
FISHNFF
Tom W Clark posted 10-02-2013 01:13 PM ET (US)
No, a 12" x 12" Stiletto Star is a 12" x 12" Stiletto Star.
A 10-1/2" x 12" Stiletto Triad is a different propeller. I might be worth trying as well.
FISHNFF posted 10-02-2013 04:40 PM ET (US)
Sorry Tom.
I read that the Stiletto Star was for pontoon boats.
Can you tell me the difference between the two, other than the obvious size difference?
Thanks,
FISHNFF
Tom W Clark posted 10-02-2013 06:37 PM ET (US)
Yes, the Star was originally designed for pontoon boats but its turns out it works very well on other small skiffs as well.
With its large diameter and low blade rake, it provides a lot of blade area and stern lift, like a four blade but without as much drag.
Your boat may not need that much stern lift, especially if the old Mercury 50 is as powerful as it seems, but I have very good luck with the Star on some Whaler applications.
The same propeller is sold as the Turbo Pontoon 1 and the Yamaha Pontoon Performance Series.
FISHNFF posted 10-02-2013 08:17 PM ET (US)
Thanks Tom. I, too, am very surprised by the little motors "punch!" But I'm sure when I add a larger fuel tank and another person, the boat will not be quite the rocket. I'll order a 12x12--FISHNFF
FISHNFF posted 10-02-2013 08:25 PM ET (US)
And regarding RPM: If I trimmed it up further, the boat felt very light and needle past 6000. The speed didn't seem to increase anymore. The motor did not totally break loose and ventilate. 5800rpm was where the boat's speed maxed.--FISHNFF
FISHNFF posted 11-17-2013 02:11 AM ET (US)
I wound up buying the 10.5 x 12 Stilleto. It is okay with my two sons, 9-gallon fuel, a starting battery, and two deep-cycle batteries up front powering a MinnKota bow mount 24-Volt Maxxum 70. On Lake Berryessa the boat planed instantly and ran up to 5,800-RPM and 35-MPH. No problem. No bow rise. No blowouts in turns. A motor just looks right with shiny stainless steel propeller.--FISHNFF

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Author	Topic: 15 Striper, 1989 Mercury 50-HP Three-cylinder
FISHNFF	posted 08-03-2013 10:52 PM ET (US) I do not have performance [data] on the [STRIPER 15 powered by a 1989 Mercury 50-HP three-cyliner enginew with] an old four-blade Comprop. What size Stilletto should I get? The 50-HP Mercury is mounted all the way down but is through bolted, top and bottom. The anti-ventilation plate is above bottom of hull about an inch. There is a 3/4-inch space between motor bracket and top of transom. --FISHNFF
Tom W Clark	posted 08-03-2013 11:09 PM ET (US) 12" x 11" Stiletto Star 3.5 Best $200 you'll ever spend on that boat.
FISHNFF	posted 08-04-2013 12:56 AM ET (US) Thanks Tom. I was thinking 13", but the extra cupping on the Stiletto accounts for that. What RPM's should that be turning? Would raising it up a set of holes help? FISHNFF
Tom W Clark	posted 08-04-2013 01:15 AM ET (US) The WOT Operating Range of the 1989 three cylinder Mercury 50 is 5300-5800 RPM. My recommendation assumes you have a 1.83:1 gear ratio, though it is possible a 1989 Mercury 50 three cylinder has a 1.64:1 gear ratio. We would need to know the serial number to pin that down.
FISHNFF	posted 09-30-2013 07:11 PM ET (US) Ran the 15 today on the Bay. Hard to start until I remembered what the previous owner said. "Squeeze bulb. Choke, no throttle." Waited, did what he said, "rrrrrrrrrrrr...Vrooom!" Short story. Prop was an old Comprop 4x10x13. The boat was a rocket out of the hole. Very little bow rise trimmed in. Almost none! Trimmed in all the way it hit 5400RPM, trimmed out where the hull came up and "lightened up", it roared to 5800RPM. Further trimming brought RPM's up without blowing out. The Quicksilver speedo read 34mph when my buddy next to me showed 30 knots on his GPS, so the speedo indicated 37mph is about right. I am very impressed. Yes, it's been a while since ive been enveloped in a cloud of blue smoke. Nostalgic. I was half hoping the motor would crap out, so I would be justified to buy a new 4 stroke. Now I just want to buy a new prop, and install a BayStar steering system. Tom, or anyone, would you recommend the same prop given my performance I experienced today? Oh, the down side. The motor drank fuel. Like almost as much as my Yamaha F115 on my 18. Oh well. Mercury 50EPLT Serial #OC226798 FISHNFF
Tom W Clark	posted 10-02-2013 11:43 AM ET (US) quote: Quicksilver speedo read 34mph when my buddy next to me showed 30 knots on his GPS, so the speedo indicated 37mph is about right. That is ambiguous. Did it hit 34 MPH or 37 MPH? 30 knots is 34.5 MPH quote: ...it roared to 5800RPM. Further trimming brought RPM's up... So what was the ultimate RPM reached?
FISHNFF	posted 10-02-2013 12:21 PM ET (US) Sorry. My speedo was reading 34 at 5400 rpmswhile I was pacing my buddy in his 16 Nausset. His GPS was reading 30.0 knots. During some WOT runs to 5800 rpms, I got the speedo reading 37mph, so I'm guessing it was pretty accurate. I did raise the motor up one hole to facilitate through bolting the lower mounts. The older Comprop, dull finish, is a 4x10x13. Great acceleration and surprisingly did not blow out in turns or when mildly trimming out. I ran around SF Bay, with all the ferry boats and tide and general slop, and boat/motor handled it fine. I am always looking for a bit more performance, and the polished Stainless "Bling". Thanks, FISHNFF
Tom W Clark	posted 10-02-2013 12:43 PM ET (US) 37 MPH is pretty darn good. I'm still not clear if you have a 1.64:1 gear ratio or 1.83:1 gear ratio. If the former, your propeller slip is about 5 percent. If the latter, the slip is about 15 percent. I am not familiar enough with Comprops to know which is more typical. I also do not know if serial number OC226798 is earlier or later than 5579017, which is the motor serial number after which the gear ratio was changed from 1.64:1 to 1.83:1 My suspicion is that you have the 1.83:1 gear ratio and based on that, and your reported top speed, you would do well with a 12" x 12" Stiletto Star.
FISHNFF	posted 10-02-2013 01:09 PM ET (US) 12"x12"? Do you mean 10.5"x12" in a Triad II? Thanks, FISHNFF
Tom W Clark	posted 10-02-2013 01:13 PM ET (US) No, a 12" x 12" Stiletto Star is a 12" x 12" Stiletto Star. A 10-1/2" x 12" Stiletto Triad is a different propeller. I might be worth trying as well.
FISHNFF	posted 10-02-2013 04:40 PM ET (US) Sorry Tom. I read that the Stiletto Star was for pontoon boats. Can you tell me the difference between the two, other than the obvious size difference? Thanks, FISHNFF
Tom W Clark	posted 10-02-2013 06:37 PM ET (US) Yes, the Star was originally designed for pontoon boats but its turns out it works very well on other small skiffs as well. With its large diameter and low blade rake, it provides a lot of blade area and stern lift, like a four blade but without as much drag. Your boat may not need that much stern lift, especially if the old Mercury 50 is as powerful as it seems, but I have very good luck with the Star on some Whaler applications. The same propeller is sold as the Turbo Pontoon 1 and the Yamaha Pontoon Performance Series.
FISHNFF	posted 10-02-2013 08:17 PM ET (US) Thanks Tom. I, too, am very surprised by the little motors "punch!" But I'm sure when I add a larger fuel tank and another person, the boat will not be quite the rocket. I'll order a 12x12--FISHNFF
FISHNFF	posted 10-02-2013 08:25 PM ET (US) And regarding RPM: If I trimmed it up further, the boat felt very light and needle past 6000. The speed didn't seem to increase anymore. The motor did not totally break loose and ventilate. 5800rpm was where the boat's speed maxed.--FISHNFF
FISHNFF	posted 11-17-2013 02:11 AM ET (US) I wound up buying the 10.5 x 12 Stilleto. It is okay with my two sons, 9-gallon fuel, a starting battery, and two deep-cycle batteries up front powering a MinnKota bow mount 24-Volt Maxxum 70. On Lake Berryessa the boat planed instantly and ran up to 5,800-RPM and 35-MPH. No problem. No bow rise. No blowouts in turns. A motor just looks right with shiny stainless steel propeller.--FISHNFF