I/O to outboard conversion

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
Hello,
I'm starting this thread because I have scoured the internet before I decided to do my conversion and very few threads ever showed the completed project.
The reason I'm doing this project is because the pilot house is perfect for fishing here in the northwest in the cold winter months but the I/O was always a PITA to winterize in preparation for the next fishing trip. (boat lives on Trailer)

My boat is a 2004 Trophy 2359 WA.

I had a 260hp 5.0 mpi w/ Bravo 3 in it and 22p props. I am converting to a Honda 250hp with a 30" shaft and a SS prop. (not sure on pitch yet as they have never had a boat like mine in for the conversion).

The bracket was built and installed by Dwayne of PDR marine in Bellingham WA. He has built and installed several of these brackets and if you look at most outboard Sea Sport boats his bracket will be on the back.
[FONT=arial, sans-serif]As for the transom: he was quite surprised on how well they built the boat. He didn't need any extra gussets or bracing for installing the bracket and did a magnificent job of glassing in the I/O hole along with all the other holes for the kicker and swim step. I also asked him to add a couple transducer brackets so I don't have to drill into the actual transom when installing the transducer. He said of cheesy plastic he'd make them better. (I think they look factory glassed in and gel coated) The bracket I chose was a full swim platform with kicker bracket and is standard for the positive flotation in the center. [/FONT]

It's currently in Oak Harbor WA getting the motor and all new digital instrumentation installed and should be completely finished in 2-4 weeks depending on parts availability. The dealer I had picked for the motor is very excited to do this as they have not had any Trophy boats getting the conversion. (I have not mentioned their name because I have not asked them if it's ok yet.)

I'm hoping I took enough data on the old motor to show any differences in the 2 but will be unable to GPH because I didn't have that on the boat and never tried figuring it out long hand.
The I/O would comfortably cruise at 30knt at 4k revs all day long. So if I get the 10% increase in cruising speed I should be able to get 33knts at 4k revs and still use less GPH. (we shall see)

As for the handling the boat with the Bravo 3 handled well and I'm hoping since the fuel tank and most of the cockpit being at or in front of center line of the boat I'm thinking it should make the Honda operate smoothly and hanging the motor farther back might actually help balance the COG better.

I really love my trophy and I wish they would have made the pilot house in an outboard to begin with but they didn't. So to find a boat even close in fiberglass and an outboard runs way more then what I paid for the boat and the new conversion / Outboard

I'll make sure to post up more pics as the boat is finished and has been run a bit to get more data on it even if it doesn't work out the way I hope. Please ask any questions I haven't answered in my long winded post and I'll really try and get pics and data up as fast as I get it.
Thanks, Joe
 

Attachments

  • photo257567.jpg
    photo257567.jpg
    316.3 KB · Views: 15
  • photo257568.jpg
    photo257568.jpg
    24.3 KB · Views: 13
  • photo257569.jpg
    photo257569.jpg
    34.2 KB · Views: 11
  • photo257570.jpg
    photo257570.jpg
    28 KB · Views: 12
  • photo257571.jpg
    photo257571.jpg
    23 KB · Views: 8
  • photo257572.jpg
    photo257572.jpg
    16.6 KB · Views: 8
  • photo257573.jpg
    photo257573.jpg
    26.2 KB · Views: 11
  • photo257574.jpg
    photo257574.jpg
    28 KB · Views: 11
  • photo257575.jpg
    photo257575.jpg
    21.2 KB · Views: 13
  • photo257576.jpg
    photo257576.jpg
    178.6 KB · Views: 11
  • photo257577.jpg
    photo257577.jpg
    133.5 KB · Views: 11

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
cool looking conversion

The I/O would comfortably cruise at 30knt at 4k revs all day long. So if I get the 10% increase in cruising speed I should be able to get 33knts at 4k revs and still use less GPH. (we shall see)

the boat with the pod on back may take slightly more hp to keep pushing thru the water than the unmodified hull simply by the larger wetted surface. your fuel consumption is based on the amount of power it takes to push the boat almost regardless of the motor pushing. 0.4 pounds of fuel per hp per hour is the standard fuel consumption of a spark ignited marine motor. dont expect a lower fuel consumption
 

ezmobee

Supreme Mariner
Joined
Mar 26, 2007
Messages
23,767
That's a really neat boat. Well worth the effort to repower how you want it and the work so far is beautiful.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
A friend of mine did the same modifications on a 23' Wellcraft WA, same motor too, use it for tuna and it works well, he eventually repowered to a Yamaha 250, both motors worked great.
 

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
cool looking conversion



the boat with the pod on back may take slightly more hp to keep pushing thru the water than the unmodified hull simply by the larger wetted surface. your fuel consumption is based on the amount of power it takes to push the boat almost regardless of the motor pushing. 0.4 pounds of fuel per hp per hour is the standard fuel consumption of a spark ignited marine motor. dont expect a lower fuel consumption

The mercruiser was 260hp at the crank and I could be wrong but was told it's about a 15-20% power reduction to spin a bravo 3. If that's accurate then I was only 210-220 at the prop and the Honda is 250 at the prop. I really hope they were right in telling me though cause I'd hate to have a dog of a boat after doing this.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
40,582
My thought is the B3 has better efficiency then a single prop. There should be a weight reduction with the OB, so hope all is good. With Honda I'm finding the 250 is the largest they make
 

bashr52

Chief Petty Officer
Joined
Aug 2, 2009
Messages
413
Here is something similar with dual outboards:
 

Attachments

  • 924789_0_090820101125_1.jpg&w=520&h=346&t=1281381930000.jpeg
    924789_0_090820101125_1.jpg&w=520&h=346&t=1281381930000.jpeg
    37.8 KB · Views: 5
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
The mercruiser was 260hp at the crank and I could be wrong but was told it's about a 15-20% power reduction to spin a bravo 3. If that's accurate then I was only 210-220 at the prop and the Honda is 250 at the prop. I really hope they were right in telling me though cause I'd hate to have a dog of a boat after doing this.

the mercruiser was rated 260 at the prop (about 290 at the crank). all boats after the mid 80's are prop rated. with only a mild cam change you can easy get 300 hp at the prop with the 5.7
 

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
the mercruiser was rated 260 at the prop (about 290 at the crank). all boats after the mid 80's are prop rated. with only a mild cam change you can easy get 300 hp at the prop with the 5.7

That's what I thought but all the Marina's I received quotes from told me that the outboards are test that way and I'd be fine with a 225 to stay at the same power but 250 would be better.

It doesn't make sense to test outboards at the prop and I/O at the crank.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,306
prior to 1981, they were both rated at the crank. the test requirement changed and the 1981 - 1985 period was a transition period. similar to the automotive rating changes
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,417
The mercruiser was 260hp at the crank and I could be wrong but was told it's about a 15-20% power reduction to spin a bravo 3. If that's accurate then I was only 210-220 at the prop and the Honda is 250 at the prop. I really hope they were right in telling me though cause I'd hate to have a dog of a boat after doing this.
You will be quite surprised how the boat will react to removing #400 from transom and the change in geometry from the bracket. Done right, should push 40 mph pretty hard
 
Last edited:

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
No Title

Update on the conversion. Motor is on waiting for parts but getting closer.
 

Attachments

  • photo257664.jpg
    photo257664.jpg
    57.5 KB · Views: 2
  • photo257665.jpg
    photo257665.jpg
    45 KB · Views: 4

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
No Title

Just a quick update. Some of the parts have been back ordered so I'm still waiting to get it on the water but that's ok. Cause it is looking awesome!! Everyone at E.Q. Harbor Marine in Oak Harbor is bending over backwards to get me the boat back and are doing such fantastic work. I've even been looking for other things for them to put on the boat because of the attention to detail is beyond premium. It'll be at least 2 more weeks before I can drive across the state to dip it but I'll get some video and pics when i do and post them up along with some #'s. Thanks for reading, Joe
 

Attachments

  • photo258627.JPG
    photo258627.JPG
    386.3 KB · Views: 6
  • photo258628.JPG
    photo258628.JPG
    312.5 KB · Views: 5
  • photo258629.jpg
    photo258629.jpg
    365.7 KB · Views: 6

hvymtl939

Chief Petty Officer
Joined
Feb 6, 2017
Messages
495
This is so awesome! The admiral and I's dream project some day is to find a Sea Ray or similar decently big cabin cruiser (28-33'), do a restoration, and convert it to OB, like the new Formula cruisers are. Can't wait to see the final results!
 

JosephPC

Cadet
Joined
Apr 13, 2014
Messages
28
No Title

Hello everybody,
Well I got the chance to test run the boat today before dragging it home. All I can really say is......... Awesome! I don't mean awesome as a loose term either. This thing is truly awe inspiring. I'm still in the break in phase and the thing will do 40 MPH without batting an eyelash. I even had one of the fish box pumps fail so I'm hauling a bunch of water around ( 32 GAL) that isn't needed and it still does great. The idle to plane is fantastic. The boat doesn't cruise at the same speed it used too but it hops on plane at half the time and feels like it's way more maneuverable then before. Cruising speed is currently down about 4 MPH at 4000 revs but this motor tops out at 6k vs the I/O at 5500 so I'm not sure if it's actually falling behind at all. I am impressed and believe it is worth every penny I dished out to get this. I will have some video links added as well to show some more performance shortly as well. The video I took today decided to cut and start a new one about 1/3 of the way into it but i'll try and post it anyway and get some more for everyone. Thanks for reading, Joe
 

Attachments

  • photo259257.jpg
    photo259257.jpg
    20.1 KB · Views: 10
  • photo259258.jpg
    photo259258.jpg
    31.4 KB · Views: 9
  • photo259259.jpg
    photo259259.jpg
    30.7 KB · Views: 9
  • photo259260.jpg
    photo259260.jpg
    28.6 KB · Views: 8
  • photo259261.jpg
    photo259261.jpg
    32.2 KB · Views: 8
  • photo259262.jpg
    photo259262.jpg
    31 KB · Views: 9
Top