Thrust of outboards

[CTD]

Is there a thrust spec on gas outboards like on electric troling motors. Reason I ask is I'm making an outboard bracket that will clamp onto my swim ladder and want to know how much push a 7 1/2 hp outboard will put out.

 

[Scaaty]

Re: Thrust of outboards

I don't think a swim ladder would hold more than 3 hp...7 would twist/bend the aluminum tube

 

[CTD]

Re: Thrust of outboards

Ladder is 1 inch stainless, holds a 225 lb man ok.

 

[JB]

Re: Thrust of outboards

Be sure to use an outboard that you can do without if you are going to clamp it to a swim ladder. Might clamp it to a swim ladder you can do without, too.<br /><br />There is a lot more than thrust to deal with.<br /><br />A good kicker/aux mount will save you a lot of grief.<br /><br />Good luck.

 

[Mike6158]

Re: Thrust of outboards

I'm no boat expert but as JB said, it's not just the amount of thrust that you'll want to consider. <br /><br />(1) Moment arm. Remember your High School physics or science class? Let's say that you want to lift something. Put a 2x4 under it and place a block near your end of the board. Now push. If the object is heavy it will not likely move. Now move the 2x4 closer to the object that you want to lift. The closer that you get to it, the easier it is to lift it. Unless the motor is mounted right on the ladder mounting brackets, the amount of thrust that the motor puts out will be multiplied by the "arm" of the "fulcrum" (actually it's a little more complicated than that because the arm of the motor is also part of the calc.)<br /><br />(2) Side load on the ladder when you turn. See item 1.

 

[CTD]

Re: Thrust of outboards

Thanks for the replies, guess that answers my question, gas outboards dont have a thrust spec.

 

[WillyBWright]

Re: Thrust of outboards

Sure would be nice if they did. But we'd have to change our whole way of relating to the amount of power they produce. I'd think the propeller used would change that anyhow. With trolling motors, the prop choice is extremely limited.

 

[walleyehed]

Re: Thrust of outboards

CTD, I don't have a thrust figure, but I can tell you my 7.5 kicker will push my 2400lb. Deep-V about 8MPH at full throttle.......Your swim ladder would be fish structure with a 7.5 clamped to it...

 

[Bradster941]

Re: Thrust of outboards

So when you fall into the water, exactly how are you going to get back in the boat?<br /><br />As JB said, use the right part for the job. Get a Kicker bracket.<br /><br />Besides, once the kicker rips your swim ladder off you’ll be to busy kicking yourself to notice the water coming in the boat from the open bolt holes below the water line from the swim ladder. <br />

 

[BillP]

Re: Thrust of outboards

I read US Navy test results for thrust on small outboards as 105 lbs for a 6hp and 218lbs for a 9.9. They didn't say what brands or anything else about the motors. They were testing against electric outboards for quiet running and noted those figures.

 

[CTD]

Re: Thrust of outboards

Thank you billp, so I can figure a max of about 150lbs and figure leverage from there. Then I can simulate that stress and see what happens. I have a nice OMC bracket with assist but it will put the kicker too deep in the water even mounted at the top of my transom and the spring is too strong for this motor. I don't know if I could push it down especially if the water is rough. I guess I could replace the plywood on it with steel plate 1 1/2 inches thick.