Choosing the right outboard for my dinghy

[firehoser75]

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.

[Tigs]

Originally Posted by firehoser75

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.

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.

[firehoser75]

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.

[Benthic2]

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.

[Tigs]

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.

[lwarden]

Is it the boat in your avatar?

[Tigs]

Originally Posted by lwarden

Is it the boat in your avatar?

yup

[Dougcole]

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.

[Tigs]

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 ?

[Dougcole]

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.

[C lectric]

If the boom itself is a single tube then consider adding a tensioner on top about 3" to 4" above the actual tube. It could be welded on of plate standoffs and a rod atop the standoffs.

Or it could be a cable with a turnbuckle for tensioning although you will still need the standoffs.

THe tensioner should be brought all the way down to just above the deck pass through.
I am not suggesting this will get you double the capacity but should add another 100 #. A good fabricator should be able to help.

As for the engine if you figure the 9HP Tohatsu is workable then get the 15hp for the same weight.

I did not have quite this problem but when I was buying our O/B for our dingbat I let my wife talk me into the 6HP Yamaha engine. It would not quite plane the boat with the two of us. I rued the decision untill it was stolen 2 yrs later, no I didn't do it, and then replaced it with the 8hp Yamaha at the same weight. World of difference.

[Soo-Valley]

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

Someone educate me at how you measure the boom load, also is the boom part of the overall 125 kilo?
My thinking is that one end of the boom is secured to the pole and the other end is attached to the pulley top of mast and to dingy lift point. Is the compression of the boom this 125 kilo?
I would think the weak link is at the mast top pulley which IMO is carrying the weight/load, which in turn anchored to the deck.

[Soo-Valley]

From a 2018 discussion that I agree is another weak link

Originally Posted by jrhodes777

I have a 1988 GB 46. Having looked into this in the past the GB published capacity is 300 pounds. However looking into it further the limiting link on my boat is the two forward shroud connections to the fly bridge rail. I am in the process of fabricating new shroud connections that will be tied onto the outside of the cabin. Overall I would suggest you look at your shroud line connections.

[Soo-Valley]

From 2016

Originally Posted by omc

Hi Bob,
About your question for the weight limit on the mast and boom to lifting a RIB tender :

In 1986 I visited the Grand Banks shipyard (American Marine LTD) in Singapore. On this occasion, I asked many questions to the technicians of the shipyard, one of my questions was the weight limit of the lift capacity with mast/boom.

The answer I got was very clear : the woody 42' GB have mast and boom made with wood, the weight limit of the lift capacity with wood mast/boom was 200 kg maximum (440 pounds). The fiberglass 42' GB have mast and boom made with ALUMINUM, the weight limit of the lift capacity with wood mast/boom was 150 kg MAXIMUM (330 pounds).

With both wood and aluminum mast/boom they told me it is very important to check the wire tension of the shrouds of the mast before operating a lift.

Fair winds,

Olivier

[Ski in NC]

With that limited hoist capacity, consider getting a lighter dink and like a 4hp motor. Sure, you can't go fast, just take your time and enjoy.

There may be a way to upgrade that lift capacity, but that can't be evaluated over the net.

Alternative is to tow the dink around most of the time, then when making a long crossing take motor off first with hoist, then lift dink. We tow ours around mostly, but for open water and high speed, motor comes off and we drag dink into cockpit by hand.

[Datenight]

Tigs,

We had Trick davits on the NP 39. The dinghy was a #120ish North Atlantic aluminum hull and the motor a 15 hp Tohatsu 2 stroke. Don't remember the weight of the motor. I could pull it up myself but was much easier if Diane helped.

Thanks for the reminder Dougcole!

Rob

[Group9]

I'd go for the 15 HP. But, the important thing is to not get one that's too big for you to handle. On our first cruise, we took an 11 foot Whaler with a 25 HP Mercury.
Pros: You could load that thing down with people and still get on plane. With just me in it, It would do over 35 mph (scary to do).
Cons: Every time I moved that motor from the boat to the dinghy, I hoped I wouldn't hurt my back.

They next trip, we took two outboards. A Mercury (Tohatsu) 3.5 HP, and a Nissan (Tohatsu) 9.8. (which would plane the Whaler, but barely) We ended up putting the 3.5 HP on 90 per cent of the time, because I could easily one hand the thing on and off the dingy. And, we found out, we didn't need to go that fast in the dinghy anyway.

All three of those motors were two strokes. I don't care for 4 stroke small outboards.

[OldDan1943]

Originally Posted by Benthic2

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

Only if you declare it.

[FlyWright]

I would definitely recommend getting the max hp the dink will support if the load isn't too much. I regularly demate my 15 hp Merc 2-stroke from my dink to lift the dink onto the swimstep for transport. Using my Garhauer lifting davit (150 lb limit), the entire launch/mount motor or detach motor/load dink process takes under 10 minutes and I don't even break a sweat. The motor travels on a fixed transom motor mount next to the dink on the swimstep.

[Crossroads]

Yes, here's another endorsement of the Garhaurer lift. I've got one in the corner of the aft cockpit for the 9.8 and a modified one on the FB deck for my PT11 sailing dinghy.