Twin Outboards?

[BuzzStPoint]

I was looking though the web at some brochures of old boats. (Glastrons) and seen some had twin outboards.

I guess my question is. Can anyone put twins on their boat? How does the HP work? Lets say you put dual 35 HP outboards on your boat. Is it as simple as you now have 70hp? Or is is still 35 HP?

 

[tashasdaddy]

Re: Twin Outboards?

70.

 

[ezmobee]

Re: Twin Outboards?

It is as simple as adding the HPs. Twins will not perform as well as a single of equivalent HP due to the extra weight and drag.

 

[CATransplant]

Re: Twin Outboards?

It is as simple as adding the HPs. Twins will not perform as well as a single of equivalent HP due to the extra weight and drag.

Yabbut twin 35s look so cool. Especially if they're a matched pair of 1958 Johnson 35s with the gold and cream cowlings. Yes!

 

[ezmobee]

Re: Twin Outboards?

Agree completely.

 

[tmcalavy]

Re: Twin Outboards?

Like this? Have since replaced the Johnson FD-11 with an RD-18 35 hp...pix to come if I can get the boat out of mothballs this weekend. Getting ready for a lake test with two 35's and one forward 9-gallon tank plumbed with a single fuel line.

 

[weekendfisher]

Re: Twin Outboards?

This can be done pretty easily to
just a matter of bolting the 2 motors on evenly spaced then joining the steering linkages and running a new dual control or having 2 single control boxes
I had considered it however the benefit of using a single larger outweighs using 2 smaller
firstly servicing costs essentially double
typically 2 smaller motors will go through more fuel than of the equivalent power
You are adding more weight
you will get a better result top speed fuel efficiency and cheaper running costs to run 1 70 hp as opposed to x2 35hp's
the only time it is really viable is if you are pretty much given the 2nd motor then I would consider it.
Cheers

 

[dwco5051]

Re: Twin Outboards?

the only time it is really viable is if you are pretty much given the 2nd motor then I would consider it.
Cheers

No, there is another time it is viable. When you are ten miles out somewhere and one of your engines fails. If that one is your only one you are in trouble.

As opposed to a twin engine airplane where all that second motor does is get you to the scene of the accident when the first one quits

 

[Fl_Richard]

Re: Twin Outboards?

Sorry DWCO - Most (if not all) twin engine craft will fly with one engine out. Just need to keep the rudder jammed to the floor

 

[dwco5051]

Re: Twin Outboards?

Sorry DWCO - Most (if not all) twin engine craft will fly with one engine out. Just need to keep the rudder jammed to the floor

Yeah, I know most twins will fly on one but most weekend pilots don't practice enough on engine out simulations. Even when they do it is mostly with power cut and a feathered prop.

I glad you said most will, remember the orginal Piper Apache with twin 125's. None but the best could get it back down safely.

 

[erikgreen]

Re: Twin Outboards?

You guys are missing out on the best benefits of having twin engines. We use them on lake superior for running dive boats.

Twins give you maneuverability... you can put one engine forward and one reverse and turn the boat in almost its own length. Very, very handy for picking up things/people out of the water, maneuvering near obstructions, or docking in tight spaces.

Second, the twins "perform" about as well as a single, but in different ways. The two props in the water give more drag than a single engine, but the twin props also give you more prop in the water usually... two 13 inchers have more surface area on the blades than a single 14.5. The result is a large amount of low speed thrust.. instant hole shot, also great for towing anything. It's kind of like the difference between a 3 bladed prop and a larger 5 blade.

As mentioned the redundancy is great, especially on a lake where you can't let the boat just drift to shore in a lot of places.

Lots of people try to say "a kicker is good enough" and it is for redundancy only.. but personally I'd mount twins for maneuverability and instant hole shot.

Erik

 

[CATransplant]

Re: Twin Outboards?

Here's a good question about twins. Suppose you have a pair of 35s on your boat. Let's say a single 35 on the same boat would hit the proper WOT RPMs with a 10.5X12 prop. Now, you add the second 35. What prop do you use on both?

I'd think it'd have to be a larger pitch by quite a bit or you'd end up at pretty much the same speed as you were going with the single 35, rather than the higher speed of a single 70 hp.

So, what's the verdict here? How do you compensate for the greater power of twins with props?

 

[tmcalavy]

Re: Twin Outboards?

I'm glad you asked Cat, cause I've been wondering about that myself with the Texas Maid. Two pix attached. These twins are running stock 10X9 1/4 props and are spaced 14 inches apart, from the center of the transom. Wondering if I'm under propped? Last time out, I was able to water-tune the carb settings well enough to get her on plane and make 28 mph carrying 500 lbs. of human cargo, 9 gallons of gas and battery. Still needs fine-tuning, but when I go aft to adjust the carbs, she wants to come off plane. I moved the nine gallons of gas forward under the bow skirt, but haven't had time or weather to test the new set up.

 

[CATransplant]

Re: Twin Outboards?

Can you scare up a couple of 11 pitch props for those? It would be an interesting experiment, I think.

I just have no idea. I've never had twins. However, I have a chance to pick up another 6hp Johnson, and I'm tempted to put both of them on the back of my 12' tinny and couple the tiller handles together. I'd just like to see what would happen, but I'd never actually run a rig like that regularly. I just want a spare engine.

But the temptation would be just too much for me.

 

[Philip_G]

Re: Twin Outboards?

Yeah, I know most twins will fly on one but most weekend pilots don't practice enough on engine out simulations. Even when they do it is mostly with power cut and a feathered prop.

I glad you said most will, remember the orginal Piper Apache with twin 125's. None but the best could get it back down safely.

not to mention the chance of a nasty failure just after rotation.

 

[tmcalavy]

Re: Twin Outboards?

Shouldn't be too hard to rig twin 6's, post some pix when you do...I'm going to start looking for set of larger props if changing the balance doesn't get and keep her on plane.

 

[Challenger84]

Re: Twin Outboards?

I'm planning on picking up another 70hp Johnson OB and was wondering if I can do this on my boat?
So I would have two 70's on a 16' bow-rider.
So both OB will equal to 140hp.
They are both from the mid 80's
So the older engines wouldn't be at it's peak hp do to age right?
maybe 120-130hp (if lucky)
The boat is rated at 115hp max.
Would this be a good idea?

 

[Fl_Richard]

Re: Twin Outboards?

NO! too much weight, too much HP not enough transom!

 

[Challenger84]

Re: Twin Outboards?

Thanks Richard!
I won't try dual ob then. lolz