Which outboard for emergency backup?

[zachduckworth]

Hi,

I'm thinking about adding an outboard to my 30' Islander to act as emergency auxiliary power and to make getting the motor onto a dinghy easier.

Last weekend I ran out of fuel while trying to motor back to the marina. My girlfriend and myself sailed back towards our slip but couldn't get there due to sailing into irons on the final leg before the channel where my slip was. We ended up docking at a nearby visitor slip for a few hours. Fortunately two buddies (real buddies) helped me get home with their dinghy. It was no fun. Also I found out that my diesel tank had a lot of gunk in it.

So, now I'd like to place a transom mount for an outboard on my boat as an emergency backup. I already carry a 3.5 Tonhatsu on my stern pulpit, so it would simply move to that to the transom bracket. This way, if I ever lose the inboard again I can deploy my outboard to at least get me the final 100 yards to my slip.

My inboard is generally in great condition, but other people around here have recently got the bug, and my fuel may be just as affected as theirs. I just added some Startron tonight, actually (after replacing both fuel filters). So I am hyper focused on my auxiliary power plan just now.

One collateral benefit will be, I hope, that it will be easier to get the outboard onto my dinghy from the bracket than from the railing. I'm youngish and in good shape and it's still perilous moving that thing around.

I may ditch the Tonhatsu also, since it isn't all that reliable itself. Hence this question. What outboard would you recommend for the dual purpose of auxiliary back up power and dinghy motor? And what bracket for a two stroke motor? The outboard will only supplement my inboard, which has been great until last weekend (partially my fault, although I think the fuel gauge may be off a bit. Thanks!

[Benz]

If you keep a small OB on a bracket near the water on a big boat, it will get a lot of salt water washing over it when sailing, which doesn't really do it good long-term. Better to keep it as far away as possible.

[Kettlewell]

IMHO get a 4-stroke and pollute a lot less and burn half as much gas. I like my 4HP Yamaha. They are heavier than a 2-stroke, but provide good thrust at lower throttle settings.

[fregata]

Apologies in advance for circumventing your question and instead addressing your justification.

I am not a fan of bracket mounted outboards. They are an economical solution and I think the list of benefits pretty much ends there. In this case, especially since you claim to have a good working inboard, consider the following:

1. Your undoubtedly stressful experience was ultimately caused by a human failure, not a mechanical one. In the future I am sure you will be more diligent about checking the fuel level in your tank having learned this lesson the hard way.

2. Your concerns about the quality of diesel can be addressed in other ways that will be cheaper and more advantageous than adding an auxiliary outboard. Consider plumbing a day tank or a means to run the engine for a short time from a portable tank of diesel that can be easily verified to be clean and not subject to potential sludge from your main tank.

3. If you are already carrying the outboard for your dinghy, then why not simply deploy the dinghy with outboard to give you the little push you need to make it back to your slip in the rare instance an event like this happens again?

My reasons for discouraging the outboard echo things other posters have said:

1. Wear and tear. Why subject your dinghy outboard to the saltwater on the bracket?

2. It is just as easy to forget to check the level in a gas tank as it is a diesel tank.

3. Limited use. Admittedly your use case is one where a bracket mounted outboard would be useful. Outside of calm sheltered waters, the prop can ventilate when the boat pitches rendering it near useless. This also brings up the point that you really need a long shaft high thrust outboard to be useful on a sailboat. This is not compatible with the short shaft version you want for your dinghy.

[thomm225]

My main auxiliary engine is an outboard which is on an adjustable bracket.

It works great especially for getting in and out of the slip.

I have had this setup for 13 years.

I use it offshore as well to get me home on Sunday Mornings if there is no wind sometimes motoring or motor sailing 20 miles.

My engine a Mercury 5 hp 4 stroke has an integral tank which is 40 ounces which gives me about 40-50 minutes motoring so I don't have to hookup the external tank.

Boat displaces about 6600 lbs. Outboard weight is 58 lbs.

Some folks have 6 hp 4 stroke Tohatsu outboards as their main engine on Alberg 30's which displace 9000 lbs.

A friend of mine actually has this setup and he recently sent me a video of him motoring into 14 knot winds out in the Bay.

Video is my 5 HP Mercury pushing boat home on a Sunday morning from about 18 miles out. Many times the wind comes up before I complete the crossing so I roll out the jib and shut off and raise the outboard.

https://www.youtube.com/watch?v=cpZhq35etcw

[Island Time O25]

On my first boat, 27 footer, I installed a transom bracket for a 9.9hp outboard to replace an old MD5A which I took out. Hated the new set up for all the reasons outlined above. Currently, on a 36 footer, I have a DIY swim platform which can act as an emergency bracket for a short shaft o/b. Have used a 35lbs thrust Minnkota on it once. Was doing somewhat ok pushing 18,000lhs+ boat in dead calms at 1.2kts. Interesting experience. Figured a 55lbs thrust woul give me 1.5-1.7 kts. ))

[Iron E]

Originally Posted by zachduckworth

Hi,

I'm thinking about adding an outboard to my 30' Islander to act as emergency auxiliary power and to make getting the motor onto a dinghy easier.

Last weekend I ran out of fuel while trying to motor back to the marina. My girlfriend and myself sailed back towards our slip but couldn't get there due to sailing into irons on the final leg before the channel where my slip was. We ended up docking at a nearby visitor slip for a few hours. Fortunately two buddies (real buddies) helped me get home with their dinghy. It was no fun. Also I found out that my diesel tank had a lot of gunk in it.

So, now I'd like to place a transom mount for an outboard on my boat as an emergency backup. I already carry a 3.5 Tonhatsu on my stern pulpit, so it would simply move to that to the transom bracket. This way, if I ever lose the inboard again I can deploy my outboard to at least get me the final 100 yards to my slip.

My inboard is generally in great condition, but other people around here have recently got the bug, and my fuel may be just as affected as theirs. I just added some Startron tonight, actually (after replacing both fuel filters). So I am hyper focused on my auxiliary power plan just now.

One collateral benefit will be, I hope, that it will be easier to get the outboard onto my dinghy from the bracket than from the railing. I'm youngish and in good shape and it's still perilous moving that thing around.

I may ditch the Tonhatsu also, since it isn't all that reliable itself. Hence this question. What outboard would you recommend for the dual purpose of auxiliary back up power and dinghy motor? And what bracket for a two stroke motor? The outboard will only supplement my inboard, which has been great until last weekend (partially my fault, although I think the fuel gauge may be off a bit. Thanks!

Your buddies got you home with their dinghy, but you have a dinghy.
Can I ask: Why can't you use your dinghy as your emergency backup?

[JimsCAL]

Generally the same outboard won't work well as both a sailboat auxiliary engine and on a dinghy. The dinghy generally needs a short shaft engine, while the sailboat needs a long shaft or extra long shaft model.

The suggestion above to consider using the dingy as your emergency backup makes sense.

[Nicholson58]

We lost the main engine diesel on our 58 foot ketch. Bad fuel, dirty filters, HP pump quit.

After cleaning, I added a fuel polisher so 100% of all fuel going to the Racor is de-watered and filtered to 1 micron. That was 12 years ago. No further problems.

[Adelie]

If I was going to use a dinghy motor to ouch that size of boat using a transom bracket I would get a Tohatsu 6hp long or extra long SailPro.

6hp is enough to push the mothership to 5-6hp.
Extra long shaft means the prop is less likely to come out of the water when waves are bigger.

SailPro gives you 3 things:
A. Small charging ability.
B. Extra long shaft
C. High thrust prop.

It’s not a real high thrust motor, the gearing is the same as the regular motor.
But the larger diameter & flatter prop is more optimized for displacement speeds so when it is pushing the mothership you get slightly higher speed for the same fuel usage it better fuel economy for the same speed.

When you put the high thrust on a dinghy the bigger flatter prop gives you better low speed thrust so you will get on a plane with a bigger load in the dinghy or it may allow you to get on a plane when you couldn’t with a regular 6hp. The tradeoff is you lose max speed so 16kt instead of 18kt or something in that range.

The fact that you already have a 3.5hp means you probably weren’t planing to begin with and planing will be a previously unavailable ability.

Just barely on a plane is the most fuel efficient planing speed.

I can see the arguments for simplicity by using the motor on the dinghy only and not having a bracket. But speed of deployment (don’t need to blow up dinghy) and easier transfer of motor from mothership yo dinghy are strong counter arguments.

OP mentioned wanting a 2-stroke. They are hard to get in the US and suffer from significantly increased fuel use unless you can get EFI.

[massnspace]

I have made several brackets for sailboats, for various reasons….made from plywood, with proper gussets, and simply dropped into place and hung off back of the boat….some I used epoxy and tape to reinforce the gussets…it doesn’t matter what length shaft you have, as long as the bracket is designed to that….

But. There is something serious to consider: How will you start it, and control the throttle? On most boats it will be very hard to lean all the way down and over to start and control it…and you NEED to have good control if coming into a marina. And you cant start the motor by pulling straight up on the cord. Needs to be a horizontal pull. I have used PVC pipe, with 4 lengthwise cuts to the end to allow it to splay out, as a cheat for throttle. You have to get the right sized pipe and then slip it on over the throttle…

I also broke my rudder cables once on a Hunter 34. Jumped into the dink, tied it to the boat, and tried to use it to move and steer the boat. It didn’t work…..boat went all over the place. Basically in circles. Finally drifted into shallow water, put out an anchor, then realized I had an emergency tiller (duh). So. Not sure if others have gotten it to work, but attaching a dinghy to the main boat to move it did not work for me.

[rslifkin]

Originally Posted by Adelie

If I was going to use a dinghy motor to ouch that size of boat using a transom bracket I would get a Tohatsu 6hp long or extra long SailPro.

6hp is enough to push the mothership to 5-6hp.
Extra long shaft means the prop is less likely to come out of the water when waves are bigger.

SailPro gives you 3 things:
A. Small charging ability.
B. Extra long shaft
C. High thrust prop.

It’s not a real high thrust motor, the gearing is the same as the regular motor.
But the larger diameter & flatter prop is more optimized for displacement speeds so when it is pushing the mothership you get slightly higher speed for the same fuel usage it better fuel economy for the same speed.

When you put the high thrust on a dinghy the bigger flatter prop gives you better low speed thrust so you will get on a plane with a bigger load in the dinghy or it may allow you to get on a plane when you couldn’t with a regular 6hp. The tradeoff is you lose max speed so 16kt instead of 18kt or something in that range.

The fact that you already have a 3.5hp means you probably weren’t planing to begin with and planing will be a previously unavailable ability.

Just barely on a plane is the most fuel efficient planing speed.

I can see the arguments for simplicity by using the motor on the dinghy only and not having a bracket. But speed of deployment (don’t need to blow up dinghy) and easier transfer of motor from mothership yo dinghy are strong counter arguments.

OP mentioned wanting a 2-stroke. They are hard to get in the US and suffer from significantly increased fuel use unless you can get EFI.

I agree with that logic. However, the high thrust prop for the 6hp Tohatsu isn't a great dinghy prop in my opinion unless you have a dinghy that's really hard to push and needs a ton of thrust to get on plane. I do keep one around for our 6hp (and it does provide better low speed thrust and much better reverse thrust). But on our dinghy, a 7 pitch standard prop for the outboard (less pitch than the original 8 pitch) is a better all around prop. It turns a bit higher RPM at WOT with any given load than the high thrust prop and it also has a higher top speed with any given load (the thick blades on the high thrust prop sap a noticeable amount of power at higher speeds, hence it turning lower RPM even though it has less pitch). Max load for planing is about the same between the 2. Acceleration rate onto plane is similar too, as the high thrust prop has so much more grip that the outboard revs up into the powerband more slowly (vs revving up faster with more prop slip during acceleration).

[Tsuru]

If it was me, I’d spend my time and money getting the fuel tank clean and the diesel reliable.

I use Star-Tron and think it’s very good as a fuel stabilizer and to minimize corrosion.
Star Tron Enzyme Fuel Treatment Diesel Additive

If you are worried about biological growth something like Biobor may be more appropriate.
https://www.biobor.com/products/biobor-jf-diesel/

[Statistical]

I would not rig an emergency outboard.

1) Your problem was avoidable.

2) Outboard is going to be ugly, put weight on the stern, not ideal for longevity in heavy seas, and likely won't be suitable for your dinghy.

3) The money would be better spent on making your diesel powerplant rock solid (to include not letting the tank get empty).

4) In a emergency use your dinghy alongside the boat for propulsion rather than trying to use the dinghy motor.

Address the root problem rather than have a hack backup. If the fuel gauge is off get the fixed, be more diligent about refueling, get the tank cleaned, and install a polishing loop. All those are reasonable low cost improvements to make the inboard bullet proof.

[NorthCoastJoe]

I would set up a day tank with Racor filtering between the main tank and day tank and a second Racor between the day tank and main tank. I have done several over these set up and no problems. Even a small day tank is good to have, you don't need anything big. My day tanks overflow back to the main, thus polishing the fuel if I leave the transfer pump on too long.


Gasoline in the USA has ethanol in it and will go bad in a short time. I use a stabilizer in my gasoline and never keep it for more than 6 months before changing it out or using it.