Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

[cobbcfi]

My bro and I have briefly talked about converting our Single screw to twin screw in order to get a little more top-end/power and fuel economy.. It seems our engine will sell for a bit less than what a 2 smaller 150s would sell for so it seems not too far out of reach.. We have an old 1983 T-Craft 24' Center Console with with a Johnson Ocean Runner 225 and only a 8ft beam.. so its kind of tight, but I was wondering what else would need to be changed in order to make this work. New Throttle stick with new cable of course, but what else? would it get expensive??
The boat is old and heavy, and we can get it up to about 35kts WOT but with about 7 people and fuel on it, 25kts WOT last week... I thought that was pretty weak and lame so I am now looking into other options..

What do you guys think??

I have added pictures of a boat that is the same as mine... pretty narrow I think for a Twin screw set-up

 

[Haffiman]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Added weight, higher fuel and maint cost ???
What prop are you running and at what rpm??
Do a test with a 4-blade prop going down 1" pitch from what you have.

 

[BonairII]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Push 3 people overboard. That should increase your top end

 

[cobbcfi]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

The engine drop down on the transom measures 55", which would easily clear twins.. We have never had but minor issues with our single but 45 miles offshore in the coming spring will be pretty regular.. Twins are a nice backup should one fail, and our boat is rated max 300hp. Dropping the 225, for a pair of 150's gives us max plus redundancy of twin screws.. After the "seacast" transom repair which is in short order, I would hate to re-drill holes for a single when twins are the answer to our problems.. And that problem is redundancy and reliability offshore without the need of the US Coast Guard or Sea-Tow..

 

[Haffiman]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

That changes totally your original reason for a change, increased speed and less fuel!
The safety of twins is a total different issue.
As for consumption you may be looking at 25 Gal/hour or 50 Gal (min) in and out. might be ok if your fuel capacity is 75 - 100 gal?
Running twin engines and for full 'separation' twin tanks might be preferable.
Hydraulic steering??

 

[cobbcfi]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

We holld 100 gallons of fuel.. Our 225 Johnson burns around 7gph at WOT, I imagine a 150 burns around 5-6gph which would mean 10-12gph with twins.. Where did you fet 25gph from? Also with twin screws we should be able to maintain cruise at a lower RPM consuming around the same amount of fuel as with the single working harder..

 

[dingbat]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Our 225 Johnson burns around 7gph at WOT,

Where did you come up with that number? That number should be closer to 22 gph. I burn a little over 19 GPH on a 200HP. Twin 150HP would suck close to 30 gph

 

[jayyyy]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Where did you come up with that number? That number should be closer to 22 gph. I burn a little over 19 GPH on a 200HP. Twin 150HP would suck close to 30 gph

X2, Carbed outboards typically burn 10% of hp/hr. So 225hp = 22.5 Gph @ WOT.

 

[cobbcfi]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Yeah, sorry that number came outta left field... Meant 22.5ish.. And were just brainstorming with this motor swap. We bought this old 83' Tcraft boat about 7 years ago and have had zero problems with it minus restoration projects. We bought it as a fixer-up and sell but have fallen in love with it so we are really getting into restoring and making it an all around better boat. From what I understand is that the Tcraft company burned to the ground in late 1983 and the molds were sold but never used again so we have one of the last Tcraft boats ever built. I really like the way its built so were just looking for Ideas.. Thanks for your help all the same

 

[Silvertip]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Speed probably will not be faster and only marginally if at all, due to the added drag of the extra motor. Hole shot may be better and cruise may be a bit more comfortable. So 30 gal/hr with duals vs 22.5 with a single for little performance advantage does not compute. Doubling maintenance costs is another consideration. The extra motor for safety is the only practical reason to do this.

 

[cobbcfi]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

So going from 225 horses, assuming its performing like new, to 300hp wont give much increase in cruise and top speed? I would have thought an increase in 75hp would give me another 5+ knots to top end and a cruise around 33-35. With the single our top speed with light load is 38kts and cruise around 25-28kts.. When were loaded with fuel, ice, and 8-10 people top speed is around 30-33kts and cruise around 20-24kts and that is stuggling to stay on plane.

 

[Haffiman]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Roughly you get about 80% 'performance' of twins compared to 'single'. In your case, 240HP single will give the same as 2 x 150 (300) twins. Has to do with added 'drag' from second engine and added weight on the transom. But it depends a lot on the boat design and balance. A narrow beam boat with less buoyancy at the stern and center of gravity further back, will 'suffer' more than a wide-hull. However a lot may be done choosing the right type of props.

 

[cobbcfi]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

The Tcraft at 24' draws 10" of water resting un-loaded and my beam is only about 7' to 7.5'.. Prolly should just stick with the single and maybe up it to a 250 or 300.. Would up-sizing the single to a larger engine give me more of what I am looking for minus the safety of have a second engine. Twins only keep you from calling the Coast Guard or Sea-Tow, I have no problem calling them.

 

[wilde1j]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Sure, a bigger single would give improved performance, compared to twins of the same total HP. Fuel use would also go up. The last few knots always come at a high fuel cost. Increase in drag at higher speeds is not linear, which is why, in your case, say a 25HP increase for a single would not yield much top speed improvement @ WOT.

You could likely get more improvement by making sure your setup is optimized. i.e. is motor height right? If it is, your AV plate will Just ride dry @ WOT in calm water. If setup needs tweaking, you can often pick up a few knots (less drag when motor is higher) and improve fuel use as well, for the same reason.

 

[Haffiman]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

A single 250-300 E-Tech would probably be the optimum. Just stay off the old V8 250-300, there you really get the fuel flowing!!

 

[BonairII]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

I would think that you're better off sticking with a single motor. You can always bolt on a small kicker motor, to get you home in case of a breakdown. JMO

The thought of burning 25gph @ $4 bucks a gallon is a bit scary.

 

[alligatorgars]

Re: Single Johnson 225 conversion to twin Johnson 150s... Good Idea???

Ive fished off of that model tcraft for years. It had a 200 yam smoker. The owner (my friend) had the floor redone and the transom then put on twin 130. I didnt get to fish on this boat after the re-rigging but I was told it was a bit faster with the twins. That flat stern really helps top end.
Clark marine
61027 North Military Road
Slidell, LA 70461-1839
(985) 649-7165
Did the work and Kenny Clark knows the T Craft 24' intimately. Give him a call with any and all questions concerning this hull. Dont be surprised if he steers you away from the sea cast transom repair.