Choosing the right outboard for my dinghy

(sorry if I'm posted this in the wrong forum)

Ok so I need to decide which outboard I need for my dinghy, headed to the Bahamas next year from my home port of Montreal. Let me know which one you would pick and why.

The Dinghy, AB 9.5 AL ... aluminum ribbed inflatable 9 feet 6 inches, weight empty 49 kilos (108Lbs) recommend 8HP Max 15HP

Dinghy and engine will be lifted by my boom onto the flybridge rated at 125 kilos (275 Lbs)

engine choice
1: Tohatsu 9.8 HP with carburetor weight of 37 kilos (81.5 Lbs)
2: Tohatsu 9.9 HP with EFI weight 43 kilos (94.7 Lbs)
3: Tohatsu 15 HP with EFI weight 43 kilos (94.7 Lbs)

The weight is important because I don't want to get close to the boom-rated lift capacity when you add besides the weight of the dinghy and engine, the oars, fuel, and anything else found on the dinghy. the boom itself is not inspiring and would like to stay far away from the 125kilo.


The dinghy will obviously be used often in the Bahamas, hence the boom will be used often too. The carb version helps me with the weight and I figure it's easier to work on it if it requires maintenance. The fuel injection version can be tricky seeing I`ll be in the Bahamas and probably far from a certified repairman. but then again I`m buying the engine new.

Is 9.8 HP strong enough for the size of my dinghy seeing I will be doing heavy supply runs?

forgot to add it will be a 4 stroke engine seeing a 2 stroke is not sold up here in Canada. I don't know if they banned them in the US.

thanks for any advice and or suggestions you might have.

(The boat a Swift Trawler 34)

Which ever one you get, one with EFI is best. Don't forget Suzuki.

We use the 9.8 on our AB 10AL. It will plane easily with two of us plus dog (total 475#).

However, I bought an EPCarry last year and find that we use it more often than the Tohatsu or rowing. Its slow (3-4 kt) with limited run time (2-3hr) between charges, but its so damn light, easy and convenient. Perfect for watering the dog 3-4 times a day.

Still, for longer runs or setting/checking pots, we use the 9.8.

Crossroads said:

We use the 9.8 on our AB 10AL. It will plane easily with two of us plus dog (total 475#).

However, I bought an EPCarry last year and find that we use it more often than the Tohatsu or rowing. Its slow (3-4 kt) with limited run time (2-3hr) between charges, but its so damn light, easy and convenient. Perfect for watering the dog 3-4 times a day.

Still, for longer runs or setting/checking pots, we use the 9.8.

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Ok so you have the 9.8 with the carb, and your dingy is slightly bigger and you say you plane easily that is good to hear, thanks for the info and the link.

Personally I would go with the 15 hp. Just because you have more hp doesn’t mean that you have to use it but when you need it you will have the power. And the weight difference is negligible.

Hi Tigs,

You'll never regret more power on your dinghy. If you can stand the weight of the 9.9 EFI Tohatsu, then I strongly suggest the 15 hp version-it weighs the same. And my choice for induction systems on outboards is fuel injection, hands down, every time.

However, I caution you to actually weigh the various components of the dinghy, including the full fuel tank, the outboard, and any other kit you plan to lug along. And, obviously, if you can't weigh the whole mess until after you buy it, you're stuck making an educated guess at the actual weight. But in my experience, the "book value" of weights for both the outboard and dinghy are understated.

On a positive note, both the Tohatsu fuel injected outboards, and the AB aluminum-bottomed dinghies are first class all around.

Regards,

Pete

I love my Tohatsu 18 w/carb but would recommend the 15 EFI.
When I bought my Tohatsu I convinced them to ship it directly to me in spite
of their policy of only selling motors over a certain size through a dealer.
That saved the price of installing it.

Found a 5-horsepower Seagull (auxiliary power for my past small cutter) at my handling limit.

I have been through several dinghies, several different outboards. Here is what I have learned.
Never settle for "just enough"
If the hoist is insufficient, change it.
If your proposed use is heavy hauling, get a bigger dinghy, even if it means towing rather than carrying.
If you think you can't afford to go to the larger, more expensive alternative, you will regret that choice.

Putting in your criteria, I would go for the max hp that will get you on a plane with your "full" load, even if the dinghy capacity plate maxes out below what you need. I did exactly that with a Caribe 10, I put on a 20, 2 stroke, and had to add smart tabs to keep it in the water, but had an awesome ride that sold instantly when I moved up.

My present Caribe 12 with a Honda 40 is another awesome ride, carries 4 on a plane, allows heavy loads on shopping trips, carries traps and a line puller,......
I can't carry anything larger, though I would trade up to a 14 or maybe bigger if I could. The ride on a longer, heavier dinghy is better, no doubt about it.
Bottom line, go as big as you can. Both dinghy and outboard.

I'm not sure how import duties would apply and I'm not suggesting you break any laws....but you could buy a 2-Stroke ouboard in the Bahamas.

https://www.hbsmarine.com/two-strokes

If you don’t have to carry it, 15 efi.

"but you could buy a 2-Stroke ouboard in the Bahamas."

The 2 strokes are the easiest to restore if the engine gets dunked.

We just went through the same thing. Our dinghy is an AB 10' AL Lamina. Weight is #128. I wanted a 15 hp Tohatsu EFI from what I have read here and other sources. When discussing the motor with the dealer (Defender) he pointed out that the weight of the 15 and 20 was the same, #95. No brainer. The boat was rated for up to 20 hp so we bought the 20.

While it cost a little more, as has been mentioned here that is gone quickly. Also, you don't have to run it on the stops! Our crane on the NP 45 is rated for #600. We should be fine there. I figure with anchor, chain and line, gas (came with 3 gal tank) life jackets the boat will be well under #300. Well within crane capacity.

Rob

You will want a planing rig for the Bahamas. There are so many cays, inlets and reefs to explore. We often spend half a day snorkeling or visiting beaches miles apart in an AB 11AL with an old Mercury 25. I would guess that we have an additional 150 lb of gear (fuel tank, 6 gallons fuel, start battery, oars, manual bilge pump, lift bridle, tow line, anchor & rode, a few tools, first aid kit, flares, nav light, water bottles, snorkeling/fishing stuff, handheld VHF, patch kit, air pump, PFD’s, bucket, some of which is water soaked).

I would be concerned about any lifting equipment with less than 2X actual load, industrial standards seem to be around 4X. There will also be dynamic loads as the dinghy swings/boat rocks due to waves, wakes and wind.

DCDC said:

You will want a planing rig for the Bahamas. There are so many cays, inlets and reefs to explore. We often spend half a day snorkeling or visiting beaches miles apart in an AB 11AL with an old Mercury 25. I would guess that we have an additional 150 lb of gear (fuel tank, 6 gallons fuel, start battery, oars, manual bilge pump, lift bridle, tow line, anchor & rode, a few tools, first aid kit, flares, nav light, water bottles, snorkeling/fishing stuff, handheld VHF, patch kit, air pump, PFD’s, bucket, some of which is water soaked).

I would be concerned about any lifting equipment with less than 2X actual load, industrial standards seem to be around 4X. There will also be dynamic loads as the dinghy swings/boat rocks due to waves, wakes and wind.

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This is my concern too, even though the boom is rated at 125kilo I'll be close to 100 no matter the engine I choose. I'm changing the cheek blocks on the boom to make it less forceful to lift but it doesn't remove the strain on the boom. I think I will try to make the first lift with it and see how the boom reacts. If it starts creaking and swaying I might have to lift the engine and dinghy separately and if that is the case I'll go with the powerful engine because the weight does not matter then. thanks for your insight

There are outboard mechanics in every nook and cranny of the Bahamas, and plenty of fellow cruisers to lend a hand too. Plus get the service manual for the engine , they are easy to DIY. You'll likely find yourself towing the dinghy more often than not.

I'd make really sure you calculate the total weight accurately.

And yes, get the 15hp.

Lifting the dingy and engine separately will be a PITA. There are many times you will want to move short distances and you may plan to just tow the dingy. From experience, light dingies don't tow very well as they can fly in wind over about 20kts - think quick thunderstorms. Get something you can lift easily and quickly in adverse conditions.
Also, if you are thinking less horsepower, I had a 9.8 AB Al rib, that came with a 6hp 4 stroke Suzuki (may have been 5). It was a single cylinder engine and would plane with about 200 lbs, but felt like a weed whacker. Sold it a week later.

Absolutely no brainer, go with the 15.



As others have said, to get the most out of the Bahamas you need a dinghy with real range. It's not like the US where you spend a lot of time in marinas or are just putting from an anchor spot to a nearby dock. There are some times when you have short dinghy runs but there will be lots of times you want to run longer distances. We sometimes put more than 20 miles a day on our tender over there, I wouldn't want to do that in a slow dinghy or one that I had to run wide open all of the time.


As far as weight goes, is 12 lbs really going to be the difference in how much your boom can handle? If that puts you over the top you are probably too close to the limit anyway.


One other tip. Through bolt the motor to the transom. The tender will run better and you don't have to worry about the clamps vibrating loose. It also makes the motor harder to steal.

TBill36 said:

Lifting the dingy and engine separately will be a PITA. There are many times you will want to move short distances and you may plan to just tow the dingy. From experience, light dingies don't tow very well as they can fly in wind over about 20kts - think quick thunderstorms. Get something you can lift easily and quickly in adverse conditions.
Also, if you are thinking less horsepower, I had a 9.8 AB Al rib, that came with a 6hp 4 stroke Suzuki (may have been 5). It was a single cylinder engine and would plane with about 200 lbs, but felt like a weed whacker. Sold it a week later.

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I understand but if towing the dinghy short distances, I'll be going no more than trawler speed of 8 knts or so I'm not too worried about it getting caught in the wind but it's certainly something to pay attention to.

Dougcole said:

Absolutely no brainer, go with the 15.



As others have said, to get the most out of the Bahamas you need a dinghy with real range. It's not like the US where you spend a lot of time in marinas or are just putting from an anchor spot to a nearby dock. There are some times when you have short dinghy runs but there will be lots of times you want to run longer distances. We sometimes put more than 20 miles a day on our tender over there, I wouldn't want to do that in a slow dinghy or one that I had to run wide open all of the time.


As far as weight goes, is 12 lbs really going to be the difference in how much your boom can handle? If that puts you over the top you are probably too close to the limit anyway.


One other tip. Through bolt the motor to the transom. The tender will run better and you don't have to worry about the clamps vibrating loose. It also makes the motor harder to steal.

Click to expand...

Lots of good points, I am going today to see the Tohatsu dealer and will confirm the weight difference like you said 12 pounds is not a lot. But the more I think about it, I will be too close to the boom limit as one member said when you calculate all the other stuff besides the weight of the dinghy and engine. Boils down to lifting both engine and dinghy separately which I'm sure is time-consuming or reinforcing the entire boom system.

Tigs,
It sounds like you are now on the right track with your thinking. The larger engine is the best choice. However, your boom setup sounds very ifffy to me. Think in terms of trying to haul your "lightly loaded" dinghy up to the top in a chop, or with a wind. It will greatly add to the loading. I am not an engineer, or even have a lot of experience with what you are proposing, but I totally agree with what others have posted. Your boom is not likely adequate.
Maybe you should consider a swim grid type of dinghy davit instead. Eg. Seawise, Weaver, or Roskelley/Olsen. All davit systems are compromising with both pros and cons. If you have to "make changes" to your existing system to make this safe and secure, you may as well look at all the options and give serious consideration to what will best (including safety) meet your needs!! I use a Seawise system, and although it does have a few "cons", for us it works fantastic. We can still access the boat using the swim grid from a dock, and we can deploy and retrieve the dinghy in less than 5 minutes with very little effort.

I would not even try your system with the weights being so close. A failure could be very costly to "fix" (meaning damage to both boat, dinghy, outboard, and gear, and that is not even considering the fact that someone could get hurt.
JMHO. Good luck.

firehoser75 said:

Tigs,
It sounds like you are now on the right track with your thinking. The larger engine is the best choice. However, your boom setup sounds very ifffy to me. Think in terms of trying to haul your "lightly loaded" dinghy up to the top in a chop, or with a wind. It will greatly add to the loading. I am not an engineer, or even have a lot of experience with what you are proposing, but I totally agree with what others have posted. Your boom is not likely adequate.
Maybe you should consider a swim grid type of dinghy davit instead. Eg. Seawise, Weaver, or Roskelley/Olsen. All davit systems are compromising with both pros and cons. If you have to "make changes" to your existing system to make this safe and secure, you may as well look at all the options and give serious consideration to what will best (including safety) meet your needs!! I use a Seawise system, and although it does have a few "cons", for us it works fantastic. We can still access the boat using the swim grid from a dock, and we can deploy and retrieve the dinghy in less than 5 minutes with very little effort.

I would not even try your system with the weights being so close. A failure could be very costly to "fix" (meaning damage to both boats, dinghy, outboard, and gear, and that is not even considering the fact that someone could get hurt.
JMHO. Good luck.

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I totally agree that is why I'm probably going with lifting the dinghy and engine separately unless I can reinforce the boom to my satisfaction. By lifting separately I'll be around half the boom's rated lift limit. Sure it will take more time but I'm I'll be in the Bahamas and time is what we have. As to having a system like Seawise, Weaver, or Roskelley/Olsen installed besides the price, I think I would need to reinforce the transom which brings in another set of problems and $$. I like the security of having the dinghy on the fly. But I do realize there are several cons to having it there and getting it there.

Yes, pros and cons.
We don't have much of a dinghy theft concern here in BC waters. It can happen, but very rare. When at home port and not aboard, I "cable lock" the dinghy to the boat, and the outboard is locked to the dinghy. However, I am aware that this "effort" will only stop the unprepared.

Can you talk to the boom manufacturer and see where the weak point is ? If you can determine that, you might be able to change the forces by adding another pully or moving an attachment point in from the end of the boom by a little. It sounds like you are getting close to the max capacity of the boom. Add some gear, a few fish and some water in the boat......and then a wake to bounce the load a little.... and you might have trouble. A boom failure ( and a dropped dinghy ) would certainly put a damper on your trip.

I doubt it, the boat is french and the boom was standard equipment probably in-house. I had trouble finding the load limit on it.

Is it the boat in your avatar?

lwarden said:

Is it the boat in your avatar?

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yup

I know this may sound crazy, and I apologize up front for spending your money, but I have been thinking about your situation.


We keep our tender (11' Caribe with 20hp Suzuki) on reinforced trick davits on our swim platform. I mostly love our set up, but it does have one downside.


Positives:


1. Pretty economical, less than $1,500.
2. Very fast, very safe launch, under five minutes.
3. Easy retrieval, less than 10 minutes for two people, maybe 15 if I do it alone.
4. You can leave the motor on and all the gear in place.
5. No motors, winches or mechanical systems to fail.



We pull our tender up onto the platform every night and seldom ever tow it. It's so easy to do, it would be foolish to do anything else.



Negative.


1. It's not as safe in a bigger following sea as storing the tender on the aft deck.



I tilt my boat up quite a bit when we are in open water and secure it with 3 ratchet straps. I've crossed the stream over 20 times with it and have had no problems. But it is always in the back of my mind that it could get pooped in a big following sea.


So that brings me to your situation. Rather than spending money to reinforce your boom, maybe add a swim platform system. When you get ready to cross, take the motor off, empty everything out of the tender and put it on the deck. When you get to the Bahamas use the swim platform system. When you cross back, put it back up on the deck.


Just a thought.

hmm, that's a pretty good idea. When crossing the gulf stream, lift everything on the flybridge separately engine then dinghy very low strain on the boom and once in the Bahamas use a traditional simple davit system, is this the system you're talking about https://www.trickdavit.com/video.php ?

Yes, that is what we have with some mods to make it stronger. I also use a block and tackle to haul the tender up onto the cradles. Our tender is pretty big.