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MA Construction


Nag Juice

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Maybe this is for Skip, but while discussing with other forum members I figured I'd post.

 

Since older MAs are still in the population, they were constructed for 2 strokes. What did MBC do to compensate for the additional weight of 4 strokes? Was the transom reinforced? I know the TM Batteries were moved forward, but I saw a picture of an older MA yesterday with a newer heavier 4 stroke. The transom was cracked. Before the tree killed my first one, I was going to repower but being it was built well before 4 strokes, I'm curious if it would've  held the additional weight or how much it would've squatted. 

 

The pictures are the same hull, just 75lbs difference in outboards. One is a 1997 the other is 2006.

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Yeeowza 160 pounds is big diff! Wondered my self as well when the time comes to repower. My 96 150 2 stroke Yamaha manual says it weighs 440 and new F150 weighs in at 480 it looks like . Thats another 40 pounds in the worst place for weight distribution for sure but not 160 pounds either. Someone suggested tossing a bag of sand back there to get an idea. few pounds to the good if the oil tank goes away too I reckon. Interesting question Nag...

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Sorry, you're right. 410 pounds was my last Motor. I must've misread the weights before. Either way, I'm curious if there was any structural differences to compensate for the added weight.  I shop for boats all the time and when I pitch MAs to people, the older engines come up with the weight differences etc. I'd like to be able to give/know concrete information about hull changes/modifications. 

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My  05 18.5 has C/K in the area of the spashwell. Don't know if that was done on all or just a few. Mine is also VARIS construction so it may be unique. 

I would think that the weight difference in engines is minor compared to the thrust and torque loads on the transom from the engine. The immediate throttle response of a 2 stroke may impart more load than the more gradual power of a four stroke. The absolute worse load on a transom has to be when your lower unit hits bottom and you come to a sudden stop. That probably accounts for more stress cracks in transoms than anything else. 

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1 hour ago, wthree3 said:

My  05 18.5 has C/K in the area of the spashwell. Don't know if that was done on all or just a few. Mine is also VARIS construction so it may be unique. 

I would think that the weight difference in engines is minor compared to the thrust and torque loads on the transom from the engine. The immediate throttle response of a 2 stroke may impart more load than the more gradual power of a four stroke. The absolute worse load on a transom has to be when your lower unit hits bottom and you come to a sudden stop. That probably accounts for more stress cracks in transoms than anything else. 

Correct me if I'm wrong, but is this really accurate?  I was under the impression that outboards are not held in their running position mechanically, they pivot freely and are kept down by weight/force.  When you run aground, the engine pivots up, minimizing the stress on the transom.  If that's not accurate, let me know.

BTW, Wthree3, sure would love to see pics of that 05 MA.  Just to drool a little.

On this topic overall, Nag and I have been arguing how much the weight actually matters (unless there is a jack plate involved), since the weight of an engine is applying downward force (vs. torque/twist) on the transom.  I would have to think that even 160 lbs of static force on the transom would be of minimal impact vs. going from a 115 to a 150 HP engine, where the force is actually putting a non-linear force on the transom.   

A jack plate would obviously change the dynamics a bit, by putting the engine weight off the back of the transom and as a result increasing the impact of the force applied by the prop.

All of these (brilliant) comments above are coming from an uneducated source and by the same brain that still thinks that electricity is completely incomprehensible, so feel free to educate me if you have facts and expertise!

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3 hours ago, wthree3 said:

Smaller outboards are free to rotate up when in forward. Except they usually have a tilt lock that engages in reverse, otherwise the motor pops up when you gun it in reverse. Large outboards are locked in position all the time via the hydraulic tilt cylinder.

The trim unit has a valve that releases pressure and allows the motor to tilt when an object is hit. I'm sure there is some stress, but it's not a direct solid immovable impact. 

I think after 04 maybe 05 all MA's were carbon fiber, I think that's kinda what killed them. The cost went up sales went down bay boats took over and the Redfisher was cheaper.

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