How low should my motor ride?

[Jimbeau]

Just finished a full trailer rework and hung a new 20hp. Question is how much clearance should the foot of the motor have from the ground? I’ve got just over 8 inches clearance with it the down position. The axle (with 12” wheels) has over 9” of clearance so maybe that’s normal, just seems low. It’s probably not a good idea to tilt the motor up for trailering? If I need more clearance I could go with 13” wheels, or make taller bunks somehow.
Thanks.

 

[onthewater102]

1st issue I see is the bunks don't extend past the transom - you're liable to end up with a hook in the bottom of your hull or worse, cracking.

2nd might be a function of the camera angle, but that motor seems to be mounted too low. The anti-ventilation plate looks to be several inches below the plane of the boat.

To answer your question, I would trailer the boat with the motor tilted up but supported by a transom saver.

 

[Jimbeau]

1) The bunks actually do extend past the transom by about 2”. I just had the boat scooted back a bit when I took the pics. I made sure of that when setting them up!

2) Well you might be right. I’ll have to check when I get home. It’s a short shaft motor. I don’t know what else to do if it’s off or how it should be set up exactly?? Never thought about that. Thanks for letting me know about this! I’d better get this right before drilling.

I’ll retake better picks with the boat on the trailer properly and also check that plate.

 

[Jimbeau]

Actually you should be able to see the trailer bunks on my second pic with the trailer hooked up to the truck. I know it’s is not the proper forum for engine height adjustments on the transom but if anyone can lend some guidance I’d appreciate it. I should probably post this topic on the proper engine forum.

 

[eeshaw]

I don't think that the motor is a short shaft 15", looks like a 20" to me but maybe it's just the pic.

 

[Jimbeau]

It’s supposed to be a short short. That’s what I purchased from my dealer. I should be able to check the specs and compare measurements. The box had been opened, so who knows..

 

[Jimbeau]

I don't think that the motor is a short shaft 15", looks like a 20" to me but maybe it's just the pic.

It measures to be a short shaft. More like 16.5” rather than the common 15” but still a SS. The model number also shows it to be a SS. Here’s a pic of a straight edge on the anti-cavitation plate.

 

[MrGiggles]

Seems awfully low to me. But check it hitched up to the tow vehicle for a real world measurement. Raising or lowering the tongue will change the height at the back as well, like a teeter totter.

The axle on your trailer is pretty far back so it would take a very tall bump or steep slope for the skeg to ever hit, but you never know. Unless the trailer is really tall, I like the skeg to be above the axle quite a bit. Transom savers are pretty cheap.

Your motor looks to be the right shaft length for the boat. After reading through your other thread, unless you're getting excessive spray or other poor handling characteristics, I would run it as is and see how it does.

 

[Jimbeau]

Seems awfully low to me. But check it hitched up to the tow vehicle for a real world measurement. Raising or lowering the tongue will change the height at the back as well, like a teeter totter.

The axle on your trailer is pretty far back so it would take a very tall bump or steep slope for the skeg to ever hit, but you never know. Unless the trailer is really tall, I like the skeg to be above the axle quite a bit. Transom savers are pretty cheap.

Your motor looks to be the right shaft length for the boat. After reading through your other thread, unless you're getting excessive spray or other poor handling characteristics, I would run it as is and see how it does.

Thanks for the advice sir. I’ll definitely check it out as is to see how it preforms. I’m also leaning towards a larger wheel and tire size to help with overall ground clearance. Transom saver is also being considered.

 

[MrGiggles]

Seems awfully low to me. But check it hitched up to the tow vehicle for a real world measurement. Raising or lowering the tongue will change the height at the back as well, like a teeter totter.

The axle on your trailer is pretty far back so it would take a very tall bump or steep slope for the skeg to ever hit, but you never know. Unless the trailer is really tall, I like the skeg to be above the axle quite a bit. Transom savers are pretty cheap.

Your motor looks to be the right shaft length for the boat. After reading through your other thread, unless you're getting excessive spray or other poor handling characteristics, I would run it as is and see how it does.

Thanks for the advice sir. I’ll definitely check it out as is to see how it preforms. I’m also leaning towards a larger wheel and tire size to help with overall ground clearance. Transom saver is also being considered.

Bigger wheels are worth looking into. Not as hard on bearings and they ride a lot better.

 

[Jimbeau]

I’ll have to cut the finder brackets off and relocate for proper clearance but I’m convinced it’s worth the trouble. Also requires new hubs to jump from 12” to 13 inch wheels. Not a problem. Hubs are are only about $35 at etrailer.

 

[JL8Jeff]

I went from the 4.8 x 12 tires to the 5.3 x 12 and that's going from around a 20.7" tire to a 21.9" tire which gives a little extra height and reduces the rpm's it's turning at. I don't think you need to change the hub for the 13" wheel if the bolt pattern stays the same as the 12" wheel. I think most 12" are 4.5" bolt pattern (for the 5 lug wheels) so as long as the 13" wheel has the same bolt pattern you should be ok. If you have the 4 bolt lug wheels it looks like they are the 4" bolt pattern and there are some 13" wheels in that pattern as well. Going to a 13" tire gives you options for around a 24-25" tall tire.

 

[Jimbeau]

I went from the 4.8 x 12 tires to the 5.3 x 12 and that's going from around a 20.7" tire to a 21.9" tire which gives a little extra height and reduces the rpm's it's turning at. I don't think you need to change the hub for the 13" wheel if the bolt pattern stays the same as the 12" wheel. I think most 12" are 4.5" bolt pattern (for the 5 lug wheels) so as long as the 13" wheel has the same bolt pattern you should be ok. If you have the 4 bolt lug wheels it looks like they are the 4" bolt pattern and there are some 13" wheels in that pattern as well. Going to a 13" tire gives you options for around a 24-25" tall tire.

-Yep, but the 5.3x12 is a biased ply. If a radial is desired it’s a ST145R12 which only slightly increase the outer diameter from the original 20.7 up to 21.3
- I thought the same about the 13” bolt pattern but I read otherwise at e trailer. I also called. They confirmed and explained that it has to do with the rim surface area. Not a big deal. My bearings and races are starting to fell a little rough anyway.
At the boat ramp today I checked out the trailer parked next to us which had ST175/80R13’s. They would look huge on this trailer.
I might have go with the biased 5.3x12 tire as you did. Gives almost a 1/2” extra ground clearance and is a nice looking tire.

 

[airshot]

Keep in mind that the taller your trailer is, the more difficult it will be to float the boat off!! In my area most ramps are shallow so we have to back in further, by having a taller trailer, back in even further! Thru my 60 years of trailering my boat, I find a lower trailer to be much easier for loading and unloading and if needed, a transom saver is a minor extra step to make the launch and retrieve much easier. Make your setup fit your needs and make it easy to use and you will find more reasons to use it more often !!

 

[eeshaw]

The picture you posted of the cavitation plate looks ok, sitting about an inch below the bottom of the hull? Not ideal, but acceptable. I try to trailer my boats so they set level when hitched up, usually takes a drop hitch since I have a 4x4. If I have to I'll even get a seperate hitch for an individual boat trailer. If the motor seems to set low and the trailer is hitched up so it sets level then use a transom saver.

 

[Jimbeau]

Keep in mind that the taller your trailer is, the more difficult it will be to float the boat off!! In my area most ramps are shallow so we have to back in further, by having a taller trailer, back in even further! Thru my 60 years of trailering my boat, I find a lower trailer to be much easier for loading and unloading and if needed, a transom saver is a minor extra step to make the launch and retrieve much easier. Make your setup fit your needs and make it easy to use and you will find more reasons to use it more often !!

Great pioneer right there! And I thought about that problem, but with all the new trailers coming with larger tires I figured there’re better. Not necessarily.

 

[Jimbeau]

The picture you posted of the cavitation plate looks ok, sitting about an inch below the bottom of the hull? Not ideal, but acceptable. I try to trailer my boats so they set level when hitched up, usually takes a drop hitch since I have a 4x4. If I have to I'll even get a seperate hitch for an individual boat trailer. If the motor seems to set low and the trailer is hitched up so it sets level then use a transom saver.

The trailer is riding about level with my 2WD truck. I’ll definitely figure out a way to mount a transom saver. I’ve also decided to mount a small Jack plate. The anti-cav plate is (like you said) only about an inch below the hull but I’m having other problems with the setup. The new motor is hitting the rev limit. It’s looking like a prop pitch issue. Figure I should go ahead and get it right while I’m at it. Once finished with the Jack plate I’ll have at least another inch clearance.

 

[LDUBS]

Jack plate and larger hubs/wheels will get you a few inches. Based on the earlier photo that isn't enough to solve your ground clearance problem. Tilting the motor up while trailering is the best solution. Glad to hear you are adding the transom saver too. Not really helpful I know. I guess I'm just blabbing. lol.

 

[lckstckn2smknbrls]

For every 1" of setback on a jack plate you can raise the motor 1/4".
My jack plate has 4" of setback, my motor is about 2"+ above the bottom of the hull.