Hermco/Suzuki question

[Old'sCool]

Merry Christmas!! I'm re-powering my 23' with Suzuki 300 and am asking a question/opinion directed at Don and others here......Suzuki is recommending two bolts on top engine mount, six total. Don, is your XL bracket good to go for another hole in that area? Any issues drilling another hole below the top set? Are others here with Suzuki 300 mounting them with six fasteners either transom or bracket?

[kmoose]

4 quality bolts on mine with no issues. I have a Hermco twin in the shed waiting for the winter.

[Snookerd]

4 bolts on mine.

[hermco]

Originally Posted by Old'sCool

Merry Christmas!! I'm re-powering my 23' with Suzuki 300 and am asking a question/opinion directed at Don and others here......Suzuki is recommending two bolts on top engine mount, six total. Don, is your XL bracket good to go for another hole in that area? Any issues drilling another hole below the top set? Are others here with Suzuki 300 mounting them with six fasteners either transom or bracket?

I would not have any qualms with adding the extra bolts although I am not sure it is necessary, Denny/Bushwacker may have some input on the engineering aspects, I would say just be sure you have the engine height dialed in before doing so or u may be drilling more holes than u need.

[DonV]

Let's see, 1/2" fine thread 316 SS bolt X 4 of them. Hummm.....I would Google the tensile stregth, shear numbers, etc., you will be shocked. It's not 7Marine 627, jeeeez

[Bushwacker]

Originally Posted by hermco

I would not have any qualms with adding the extra bolts although I am not sure it is necessary, Denny/Bushwacker may have some input on the engineering aspects, I would say just be sure you have the engine height dialed in before doing so or u may be drilling more holes than u need.

Don's right, focus on getting the engine height correct first! Although the 23 is a different animal, my experience on a 20 is that AV plate will need to be almost 6" above keel to get AV plate above clean water, so you may need a jack plate to get it high enough.

Regarding bolt strength, 6 bolts is rather serious overkill! Although I would defer to the opinion of Capt. Terry, who was much more of a "hard metal" mechanical engineer than me (I specialized in the "hot air" heat transfer/thermodynamics end of the business!), my take on it is that 4 bolts are more than adequate. Per the Marx Mechanical Engineering Handbook, 4 Grade 5 1/2-13 UNC bolts are very conservatively good for a working stress of at least 85,000 PSI at a proof load and 120,000 PSI ultimate stress. This translates to a proof load of about 4800 lbs for 4 bolts; any higher than that and they'd start to stretch, but they'd go up to about 6800 lbs before they'd break. That means you could lift your entire boat with just those 4 bolts! If you wanted even more strength, Grade 8 bolts are good for 150,00 psi ultimate and high carbon Cro-moly steels are much stronger than that, but you may have trouble finding stainless Grade 8 bolts.

The main thing is to just make sure the bolts are torqued evenly and correctly with an accurate torque wrench. (I don't trust the fancy click-stop type because you have no way of knowing if they're out of calibration! With the simple direct reading beam-type, if it doesn't read 0 with no-load, it's real obvious if it's been over-torqued! Mine reads about 12 ft-lbs with no load on it, but it's real easy to compensate for that!)

[Old'sCool]

Thanks to all. The engine height would need to be correct first for sure.

So Don, If I decide to add two additional is that area of the bracket the same configuration as where the other holes are? Your bracket came pre-drilled so I never saw chips.

[kmoose]

On mine I plan to test fit the bracket and motor on the current transom prior to the rebuild to help determine the optimal mounting for each. This will allow me to run the boat with the bracket mounted to Don's specs and see if I can get the motor at the right height and test it under load with my standard crew and gear. My goal is to not need a jack plate for the 30" Zuke considering I got the double bracket.

Considering the Zukes like to run a little deeper due to the large prop size I am optimistic the specified bracket mounting location will put me in the zone where I don't need to mount the bracket higher than specified. Is there any serious consequences if it has to be mounted an inch or so higher?

[77SceptreOB]

Originally Posted by kmoose

On mine I plan to test fit the bracket and motor on the current transom prior to the rebuild to help determine the optimal mounting for each. This will allow me to run the boat with the bracket mounted to Don's specs and see if I can get the motor at the right height and test it under load with my standard crew and gear.

Very smart approach.

[Bushwacker]

Originally Posted by kmoose

. . . Is there any serious consequences if it has to be mounted an inch or so higher?

You'll lose some buoyancy, and since the whole point of running the twin bracket is increased buoyancy, I'd think you'd want to avoid raising it. Generally you want to mount the flotation tub as low as possible to maximize flotation/self bailing, and I think Don has that dialed in very well, so I'd try to mount it per Don's recommendations. Motor height is a separate issue and best handled with a minimum setback manual jack plate, or some fixed brackets once you have the height dialed in.