Jump to content

Twin 9.9 Suzuki outboards on a 16 ft Sylvan


Flygaff

Recommended Posts

I just finished the bulk of the work on my 16 Sylvan Pro Select. NJ has HP restrictions on many of the lakes I fish. 9.9 Max. They don't seem to mind if I use more than one. For years I have been running Twin 1995 Evinrudes upgraded to 15 HP. What I did here is buy 2 2021 Suzuki 9.9 and upgraded them to 20 HP each. It was a very simple upgrade. I first used a single 9.9. on my 16 Sylvan I only had 7.5 MPH.  I then upgraded it to a 20 HP. With single engine the speed went up to only 9.5 MPH. So, I bit the bullet and purchased a 2nd 9.9 and upgraded it to a 20 HP. What a Change. With the Twin 20 HP Suzuki outboards I now can hit 28 MPH. Wow, what a change. Still doing some tweaking to get things right. One issue I  am having now is I get a large rooster tail between the engines.  It is a problem.  Lots of water shooting up and into the transom area. Plus I would think it is a large drag that may slow me down. I can't seem to find a reason for the Rooster tail. Any Suggestions?

 

Regards

 

Bryan

Link to comment
Share on other sites

The extra weight of the second engine probably changed the weight balance enough for the boat to go up on plane and that makes a world of difference. There is a good chance that with only one 9.9 engine with the weight properly balanced (less up front more in back)and the motor properly trimmed you would make it up to 15 mph.

The rooster tail happens because of too high trimming and /or too much water being pushed out and the air having less resistance than the water.

The idea of using only 9.9 or less has a lot to do with keeping the lake clear of exhaust and noise pollution.

You may or may not have found a legal loophole in the rule of this law, but the spirit of that law is breached.

 

Edited by rolmops
Link to comment
Share on other sites

did you keep the anti-cavatation plates even with the deadrise of the transom?the anti-cavitation plate is supposed to be even with the keel of the boat.with you going with twins,the motors are now outboard of the keel,so higher up on the dead rise of the transom,thus the motors are too far in the water when on plane causing your rooster tail???

Link to comment
Share on other sites

1 hour ago, rolmops said:

The extra weight of the second engine probably changed the weight balance enough for the boat to go up on plane and that makes a world of difference. There is a good chance that with only one 9.9 engine with the weight properly balanced (less up front more in back)and the motor properly trimmed you would make it up to 15 mph.

The rooster tail happens because of too high trimming and /or too much water being pushed out and the air having less resistance than the water.

The idea of using only 9.9 or less has a lot to do with keeping the lake clear of exhaust and noise pollution.

You may or may not have found a legal loophole in the rule of this law, but the spirit of that law is breached.

 

Yea, I’m pushing the spirit a bit. From an environmental standpoint I’m ahead of the game going from twin 15 hp 30 year old two strokes to twin 2021 four stroke. But the real issue is safety. The lake I fish blows up fast and at 8-10 mph your a sitting duck. They lose people in weather there almost every year. Also I need the extra power for fishing the Delaware river. Most of my fishing is in elec only lakes. 

  • Like 1
Link to comment
Share on other sites

40 minutes ago, finsntins said:

did you keep the anti-cavatation plates even with the deadrise of the transom?the anti-cavitation plate is supposed to be even with the keel of the boat.with you going with twins,the motors are now outboard of the keel,so higher up on the dead rise of the transom,thus the motors are too far in the water when on plane causing your rooster tail???

That may be the issue. I hade twin 15s on their in the past with no issues but they were older engines. I’ll have to look at my options. I don’t believe there is a way to raise them up higher. Fun project anyway

Link to comment
Share on other sites

10 minutes ago, finsntins said:

just like big motors,smaller motors come in different length shafts,short or long,i believe short shaft little motors are 15" and long shaft are 20"

Yea they are 20 inch

Link to comment
Share on other sites

20" might be good if it was a single engine setup,dead center on the transom,but you may need the short shafts with the twin motor setup.im just guessing here,you will have to see where the plates are in relation to the bottom of the transom.

Link to comment
Share on other sites

I had twin 1957 Johnson 35 hp sea horse engines on my 1957 Herter's 16 footers. (I know, I predate Dinosaurs and I knew young Ole Evinrude when he was a child). I had the splash problem and the tiger tail as well.

So I went to Bill Mayer of Mayers Marina in Webster and asked how to solve the problems.

He told me that because of water resistance to multiple lower units you can only expect a 35 % increase in power when using twin engines. The splashing and tiger tail problem are solved by trimming the engine a bit farther down which raises the stern a bit and the tiger tail will also become less that way. In addition he told me to have the engines face sideways just a bit so instead of one straight backward water stream you get two more separate streams. He warned me to be very careful with the down trimming because it pushes the bow down a bit and to never make sharp turns because of the engine angles as one of the engines may come out of the water a bit too much.
Old Bill used to race boats in the fifties.

Edited by rolmops
Link to comment
Share on other sites

22 hours ago, finsntins said:

20" might be good if it was a single engine setup,dead center on the transom,but you may need the short shafts with the twin motor setup.im just guessing here,you will have to see where the plates are in relation to the bottom of the transom.

Yea, I need to get the engines up a bit. About 3 inches. I just bit the bullet and ordered two TH Marine Mini Jack Plates. You can go up as high as 5 inches and it sets the motors back 4 inches. I'm pretty sure this will cure all my ills and give me a little extra speed. $150 for each bracket. now I just have to pull two engines and drill a bunch of new holes in my transom. 

Link to comment
Share on other sites

2 hours ago, finsntins said:

there ya go,it will definetly give you little more speed cause of the less drag,good luck with your project!!!!

Thanks Fin

Link to comment
Share on other sites

On 1/5/2022 at 4:38 PM, finsntins said:

there ya go,it will definetly give you little more speed cause of the less drag,good luck with your project!!!!

I just received a pair of TH Marine Mini Jack plates. It will give 4 inches of lift and a 4 inch setback for each engine. Now my question is, How close together should i mount the engines? I currently have them at 24 inch centers. I'm thinking of bringing that down to 17 inches. Any thoughts?

 

Thanks

Link to comment
Share on other sites

I understand your concern for safety with the twins.  I was down the far east end of the valley a couple of years ago during a weekday with no one around coming into a stiff west wind with whitecaps and 3 miles to go to get to the launch ramp when the engine quit.  Good to have that spare.

Link to comment
Share on other sites

On 1/17/2022 at 11:12 AM, cr3 said:

I understand your concern for safety with the twins.  I was down the far east end of the valley a couple of years ago during a weekday with no one around coming into a stiff west wind with whitecaps and 3 miles to go to get to the launch ramp when the engine quit.  Good to have that spare.

Ive been out there on 3 days when  summer storms popped up without much waring. All three times at least 1 boat sunk. I have also towed boat in as storms approached. Safety is key. A little extra speed helps as well

Link to comment
Share on other sites

  • 2 months later...
On 1/20/2022 at 11:15 AM, Flygaff said:

Ive been out there on 3 days when  summer storms popped up without much waring. All three times at least 1 boat sunk. I have also towed boat in as storms approached. Safety is key. A little extra speed helps as well

I finished the project and raised and tweaked the engines a bit. With 4 batteries and two people in the boat I was able to hit 27.8 mph. More than I expected. Now I have to mount my motor guide 24vlt motor and run the wires

Link to comment
Share on other sites

My boat is 16'11 with a 9.9 Suzuki and a 90HP Mercury. I fish restricted lakes with just the electric or the 9.9 all the time and the cold Merc just steering, I did try a 20hp computer on my last boat with a similar 9.9 engine it didn't plane with the extra HP so I swapped props for a month and I got like 2mph for my $1000 so I'd never do that again. I got a ticket once I was 6 miles from the launch and it appeared to be a tornado blowing down the lake. I fired up the 90HP and hauled away from the incoming doom, then continued on to the launch but the warden was down there too where it was pretty clear. Nice guy actually I admitted guilt he went easy on me. There's no law in NY against having a motor that's not used. Hull speed is like 7 or 8mph that's all I got on the restricted waters.

Link to comment
Share on other sites

  • 1 month later...

Well I finished the twin 9.9 project. I'm mostly happy with the results. My final numbers are: With 2 people on board, a full bag of fuel, the trolling motor, and A pair of Canon elec downriggers, I am able to run at 24.4 MPH. with just myself in the boat I briefly hit 28 but mostly its at 27.6. Now I can try out other lakes and not be crawling along at 10 MPH. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...