Long shaft on a Squirt

Outboard designs up to 14'

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jeff k
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Long shaft on a Squirt

Postby jeff k » Thu Apr 02, 2015 3:15 pm

Has anyone run a long shaft on a Squirt? I have 3 suitable motors for mine but they are all long shaft. I can raise the transom height without a problem as the boat is still under construction. The other option is to use an aluminum set back, riser plate that bolts to the transom. This would raise the motor 4 inches, and set it back 4 inches. Just kicking around some ideas here and looking for input from Squirt builders.
This boat project is destroying my wallet, But it is enriching my soul.

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areame
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Re: Long shaft on a Squirt

Postby areame » Thu Apr 02, 2015 6:53 pm

I'm putting a 1957 18 hp on mine and it has a shaft length of 17-18". I raised my transom enough to compensate but I'm not sure what effect it will have on the steering setup.

As for the jack plate I saw another Squirt builder do this but I'm not sure if they reinforced the transom, or if you would even need to.

Hercdrvr
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Re: Long shaft on a Squirt

Postby Hercdrvr » Mon May 11, 2015 1:26 pm

I'm hanging a 1967 33hp Evinrude short shaft on my squirt (I'm know, I know, pushing the limits of a squirt) the cavitation plate is about 2" below the bottom of the boat with a stock height transom. I'm not going to modify the height. Planning to launch 1 June, I'll let you know how it performs. My thinking is, raising the motor will put the motor clamps scary close to the top of transom.
Matt
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jeff k
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Re: Long shaft on a Squirt

Postby jeff k » Thu May 14, 2015 11:38 am

I'm pushing the limits a bit myself. I'm starting out with a 92 30hp. evinrude. Just worried about the long shaft. I can raise it 4 inches without modifying the transom height with a set back plate. I guess we will see how it handles it.
This boat project is destroying my wallet, But it is enriching my soul.

Hercdrvr
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Re: Long shaft on a Squirt

Postby Hercdrvr » Sun May 17, 2015 10:20 am

Areame, I'm hoping the added drag with shaft deeper in the water will make the boat more stable. How much does your 92 30 hp weigh? My 67 33 hp is 135 lbs. I'm mounting the gas tank and lawn tractor size battery in the bow. 6 gallons of gas + 15lb battery....=about 50lbs with a 7ft lever vs 135lb motor with a 1ft lever from transom. 50lbs wins on the teeter totter.
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Hercdrvr
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Re: Long shaft on a Squirt

Postby Hercdrvr » Sun May 17, 2015 10:22 am

Jeff k, sorry, I thought you were Areame

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Andy Garrett
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Re: Long shaft on a Squirt

Postby Andy Garrett » Mon May 18, 2015 8:46 am

Gentlemen,

If I may...

Transom hieght is measured vertically as the motor hangs. You may ignore the measurement from top of transom to bottom edge as it conforms to the transom angle. This number will be off.

Also, remember that some motors don't conform to the the 15 or 20 inch rule. The only accurate way to do it is to actually measure from the rear of the 'U' notch in the motor clamp to the catatation plate. Whatever this number is; 15", 20", 17.5", whatever..., that should be the vertical distance from the rear edge of the upper transom to the line where the bottom of the transom is in line with the keel.

Method:
Tape a yard stick to the bottom of the hull along the keel. Leave a foot sticking out the back. Use a plumb bob and/or another yard stick to measure the distance vertically from the rear upper edge to the appropriate spot on the taped yardstick. This is should be the exact number as the measurement obtained from your motor.

If it's off either way, shim or trim as needed. You can easily laminate more wood to the top with epoxy and even screws if you like. The easiest way is to make the transom a little tall and once the boat is righted, test fit the motor and trim the upper edge carefully until a yardstick reveals that the keel and the cavataion plate are perfectly alligned.

I waited until my motor was in perfect position, then I drilled my bolt holes right through the mount while the motor was hanging and clamped firm. That way I knew it was perfect.

A motor too deep will have a dramatic impact of performance. I see no reason why it would 'stabilize' the boat. I foresee a far less controllable boat with far less speed and efficiency.

Just my two bits.
Andy Garrett

Perhaps the slowest Zip build in Glen-L history...

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Andy Garrett
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Re: Long shaft on a Squirt

Postby Andy Garrett » Mon May 18, 2015 8:50 am

Also,

The long shaft motors are typically easier to set up for steering because you won't have to wrestle with routing cables through the sides of the motorwell--you can go right through the deck where convenient.
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Perhaps the slowest Zip build in Glen-L history...

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galamb
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Re: Long shaft on a Squirt

Postby galamb » Mon May 18, 2015 6:47 pm

The question often comes up.

From a mechanical stand point there is no reason you can't use a long shaft on a short shaft (sized) transom.

From a performance stand point the "average" boater would not notice any decrease in performance.

What it does do:

It creates a little more drag (so a little more fuel burned and a little less top end speed) since you have more hanging down below the bottom of the boat, but we are talking small numbers here.

It is a little heavier, again, depending on the motor because after all you have 5 more inches of metal, driveshaft etc.

It means you have to be a little more careful in shallow water because again, you have 5" more "stuff" below the hull that wouldn't be there if the motor was mounted at the correct height - so watch for bottom, rocks etc.

It has way less chance of cavitating and "sucking air" because the pick-up for the cooling system is "way below" the water line.

You could alter the transom (in the building stage) or add a jack plate or an elevator plate (afterwards) OR you could simply "strap her on" and go boating unless you are trying to squeeze every last bit of performance from your set-up.
Graham

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Hercdrvr
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Re: Long shaft on a Squirt

Postby Hercdrvr » Mon May 18, 2015 11:48 pm

Galamb ,
Well said, it's not the end of boating utopia if the shaft is digging in a few inches too deep. My concerns are, I've hung a big engine on a squirt and...
1. Adding height to transom multiplies the stress on it. Transom knee gets farther away from point of max stress.
2. I've read threats about "Jack plates" , it only moves weight aft and the point of torque on transom up, away from the transom knee.

Had I known what a good deal of an engine I would stumble on in the beginning, I would have modified transom to a specific shaft length, but blocking up the stock transom like a lifted 4X4 is giving the torque of the motor the upper hand against the transom.

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Andy Garrett
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Re: Long shaft on a Squirt

Postby Andy Garrett » Tue May 19, 2015 6:46 am

Why does there have to be any additional length below the boat?

Many builders have done this. They just build the transom 5 inches higher. If stress is a concern, build a taller knee to compensate, but having built a Zip the same way, I can say with authority that this type of design with a motrowell tied in is far above the minimum stregth needed--especially for a smaller engine as would be installed on a Squirt.

I just think that you might be making performance sacrifices for the sake of strength when you don't need to.
Andy Garrett

Perhaps the slowest Zip build in Glen-L history...

gdcarpenter
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Re: Long shaft on a Squirt

Postby gdcarpenter » Tue May 19, 2015 2:51 pm

My two cents.

Raising the height of the transom to accommodate a long shaft on a boat designed for a short shaft increases the 'torque' stress the engine places on the transom, simple leverage principal. How much? That's the $24,000.00 dollar question, and as I am not a naval engineer, cannot assess. And you want to use triple the horsepower rating recommended?

As for running the cavitation plate a bit deeper - if memory serves me correctly "Buddy Slack" built a significantly modified ZIP, in a 'Gentlemans Racer' style. He has run at least 70 HP on it and I'm sure he mentioned that the deeper cavitation depth on one of the larger engines he ran helped the stability of the boat, which seems logical, with the caveat that it does crest a tad more 'drag'.

I think of the Cathedrals with the Flying Buttresses in Europe. Apparently they kept building them lighter and lighter until one collapsed, then they knew they had reached their limits :)
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redoak
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Re: Long shaft on a Squirt

Postby redoak » Wed May 20, 2015 3:37 pm

The forces applied to a transom from an outboard are usually misunderstood. Most think the outboard will rip the top of the transom off the rear of the boat. This is a misnomer. When an outboard pushes a boat through the water the stresses are on the bottom of the motor clamp/plates pushing INWARD. The outboard pushes the boat forward. The boat, because of drag pushes back on the lower half of the motor plate. Look at any clapped out rotten transom glasser and you will see what I mean. The transom failures are always from the BOTTOM of the motor clamp plates pushing through the center of the transom. The stresses at the TOP of the transom are the smaller force. The top of the transom is the "lever point" NOT the stress point. If you run the long shaft you would need to beef up the point where the lower point of the clamp bracket contacts the transom. Do this by increasing the size and height of the brace. Add 1/2 inch to the depth of the transom brace where the bolts go through both at the transom and where they attach to the keel. Add the same amount to the height and length of the transom brace to get the bolts through the transom to the center point between the top of transom and the lower contact point of the motor clamp plate. Any Engineers in the audience want to chime in here on my theory?

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jenko
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Re: Long shaft on a Squirt

Postby jenko » Thu May 21, 2015 3:20 am

well this is how I see the effect of increasing the leg length given the squirt weighs 120lbs in order to move it 120 lbs thrust at prop which pushes at lower mount and opposite force at upper mount, times leverage.
Also need to figure in the force of the engine weight ,wanting to stay where it is when you accelerate, pulling at the transom top
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jeff k
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Re: Long shaft on a Squirt

Postby jeff k » Thu May 21, 2015 3:36 am

Excellent diagram jenko. What would the outcome be if the transom height was raised 4 inches? Would that cancel out some of the additional force applied?
This boat project is destroying my wallet, But it is enriching my soul.


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