In between a long and standard shaft - which to choose ?

[Ironhorse2022]

The 84 Suzuki 30 hp on my 14’ aerocraft (15” transom) is a long shaft. The cavitation plate is 2” below the floor of the boat and 1” below the bottom of the keel. I’m expecting a standard shaft to be 5” shorter than my motor which puts the plate 3” above the transom floor. I’m aware that a 15” transom typically takes a standard shaft motor. I’m just not sure 3” above the transom floor is right. Your thoughts ?.

 

[airshot]

Are you measuring with the cav plate parallel to the bottom of the hull ?? Transoms and motors are typically 15" or 20"

 

[LDUBS]

I have the same thought at Airshot. From you comments I think you already know this, but here is a pic that shows the concept.

 

[thill]

You need either a short shaft or a mini-jacker jack plate. I'm here because I just bought a boat that needs a mini-jacker to fit the motor that I have for it

 

[Stand Up]

I have the same thought at Airshot. From you comments I think you already know this, but here is a pic that shows the concept.

Thanks for posting up this diagram. It shows where the motor should be or look like when correctly mounted. Really, I had no idea about this. I'm learning a lot on this forum.

 

[DaleH]

Mount vent plate even with to 1” above (preferred) bottom of the hull for best performance. Fhughedabout where the floor is - zero bearing on this factor.

Never go lower IMHO - never have - never will - from setting up dozens & dozens of skiffs.

 

[Ironhorse2022]

Thanks all. Yes, motor is vertical and AV plate is 2” below the bottom surface of the hull (reference picture posted by LDUBS). I do have a keel ridge that extends another inch below the bottom of the hull so my AV plate is 1” below the keel bottom. I’ll look into mini-jackers. seems clear I should be targeting 0-1” above bottom of hull. Any other negatives to having a long shaft on a 15” transom assuming AV plate is positioned correctly ? Thanks again.

 

[DaleH]

Any other negatives to having a long shaft on a 15” transom assuming AV plate is positioned correctly ? Thanks again.

Not a negative UNLESS they won't clamp ... but make SURE the mount clamps securely holds it to the transom and if possible, consider adding a thru-hull mounting bolt, once you are satisified with the height.

 

[Ironhorse2022]

Got it. Already have 2 thru- hull bolts below the clamps. Will make sure to repeat if I end up with a jacker.

 

[lckstckn2smknbrls]

I have an 83 Mariner 25hp short shaft that is a long short shaft.
I run a T and H mini jacker and have the motor about 2 inches above the bottom of the hull.

 

[airshot]

Forget about having the motor verticle, that has no bearing on install...the cav plate needs to be parallel to the boat bottom !!! Put a long straight edge on the cav plate then tilt the motor until the straight edge is parallel to the bottom of the hull !! Once the cav plate and boat bottom are parallel then measure height above or below the boat bottom ....Now your cav plate needs to be at or slightly above the bottom of the hull, forget the keel. Use your straight edge to get your dimensions..

 

[Ironhorse2022]

Perfect, thanks airshot. Appreciate your input T - will look at that brand of jacker.

 

[Ironhorse2022]

I found one of these for sale near me. Anybody know if it’s a good one ? I believe it’s rated for 225 HP so should handle my 30 fine. I’m hoping there’s a way to lock it in once the height has been adjusted - wouldn’t want to rely on just the jack screw.

 

[thill]

That is a big, heavy jackplate, and it looks like a 4"-6" setback. How big is your boat? That may throw off the balance of your boat, both in weight and geometrically. It is certainly way too big and heavy for my 1648.

I'm pretty happy right now. I just found a "short shaft" motor for mine, and it's around 17" from transom top to anti-ventilation plate. Still a little long, but much better than the 22" long shaft. I plan to put a 1" block on top of my transom, and that should suffice for now.

Maybe I'll get a mini-jacker in the future, if I'm not happy with the performance. I had one on another boat, and it worked great.

Here is the T&H mini-jacker. As you can see, it's pretty simple and much lighter than a full jackplate:

 

[JL8Jeff]

You could do the TH Marine CMC riser plates.

 

[Ironhorse2022]

My boat is 14’ w a 30 hp. Boat alone weighs 180 lbs plus 80-100 For the motor. I bet your right about the Jackplate I found being way overkill. It is a 6” offset which didn’t seem like much to me. I don’t understand how artificially moving the transom back can negatively impact handling. I like the look of those cnc plates. It kills me to spend $200 on something that looks like I could make it out 3/8 wall alum angle iron.

 

[LDUBS]

Here is some "blue sky" stuff. I say that because I'm no where near an expert on this stuff. Can you raise the outboard the needed distance without using a jack plate with an offset? It seems something like JL8Jeff posted in #15 would allow you to raise your long shaft with very little added set-back. I have no idea on the pricing for something like that. Fabricating one seems pretty straight forward too.

 

[Ironhorse2022]

Yes, I agree that Jeff’s #15 post seems like a good approach. Add a nice laminated section of wood between those angle irons for the motor to clamp to. My favorite idea so far.

 

[LDUBS]

Yes, I agree that Jeff’s #15 post seems like a good approach. Add a nice laminated section of wood between those angle irons for the motor to clamp to. My favorite idea so far.

Out of curiosity I went to a site for that CMC riser. Pic I saw didn't use any wood. The motor mounts right to the upright angles -- says the set-back is 1/2". They do look pretty beefy.

 

[JL8Jeff]

Here's a set on Ebay for a decent price.

5" Outboard Moter Riser Plates - Osemar | eBay

This Osemar Jack plates are used to raise the motor of a boat higher. Outboard motor riser plate allows the motor to be mounted 5" higher than the standard mounting height on the transom. Outboard Jack Plate is made of 0.5‘’ high strength polished Aircraft Quality Aluminum.

www.ebay.com