Planing Dinghy: Hp vs Dinghy type vs #Passengers

[Adelie]

My reading of the data is that hard and folding dinghies will get on a plane with 1 more person than any inflatable for a given HP.

Since I don't believe that there are any soft floor inflatables available anymore for motors my assertion that they are the worst for drag is not supported in the data. It is supported by the fact that no one offers soft floor for motoring anymore.

I don't see any distinction between RIBs and other inflatables. Given the lack of control on weight per person that is in the data that isn't surprising.

What I'd really like to do is get $10k, buy some inflatables & motors and test them with varying weight. Maybe when I retire in a decade.

[wingssail]

Originally Posted by Jammer

So, conclusions?

- Planing performance is mainly about combined weight of the boat, motor, and people, and less about boat shape and construction.
- 6hp provides marginal planing performance, for one person and a small dinghy
- 8hp not much info, in the USA these are all derated 9.9hp and no one buys them.
- 9.9hp provides adequate performance for two people in a small boat.

Since weight is a primary factor, I offer this rundown of what is available:

9.8/9.9 HP
Tohatsu 2-stroke 57 pounds
Tohatsu 4-stroke 81 pounds
Yamaha Enduro 2-stroke 84 pounds
Honda 4-stroke 92 pounds
Yamaha 4-stroke 92 pounds
Suzuki 4-stroke 97 pounds

15 hp
Yamaha Enduro 2-stroke 84 pounds
Tohatsu 2-stroke 90 pounds
Tohatsu 4-stroke 95 pounds
Honda 4-stroke 104 pounds
Suzuki 4-stroke 105 pounds
Yamaha 4-stroke 132 pounds

18 hp
Tohatsu 2-stroke 90 pounds

20 hp
Tohatsu 4-stroke 95 pounds
Honda 4-stroke 104 pounds
Suzuki 4-stroke 105 pounds
Yamaha 4-stroke 146 pounds

25 hp
Yamaha Enduro 2-stroke 117 pounds

Hmmm? Must not like Mercury.

[Jammer]

Originally Posted by wingssail

Hmmm? Must not like Mercury.

Same weights as Tohatsu and most of the parts interchange. Around here the ones being sold mostly have Tohatsu stickers on them.

[rslifkin]

Originally Posted by Jammer

Same weights as Tohatsu and most of the parts interchange. Around here the ones being sold mostly have Tohatsu stickers on them.

Only for the newer units. Older small Merc outboards aren't rebranded Tohatsus like the current stuff.

[wingssail]

Originally Posted by Adelie

My reading of the data is that hard and folding dinghies will get on a plane with 1 more person than any inflatable for a given HP.

Since I don't believe that there are any soft floor inflatables available anymore for motors my assertion that they are the worst for drag is not supported in the data. It is supported by the fact that no one offers soft floor for motoring anymore.

I don't see any distinction between RIBs and other inflatables. Given the lack of control on weight per person that is in the data that isn't surprising.

What I'd really like to do is get $10k, buy some inflatables & motors and test them with varying weight. Maybe when I retire in a decade.

Well, with $10K you could buy about one dingy motor set-up.

As for soft floor inflatables I'd have to think that "air floor" boats should be included. As a planing boat they are much worse than a RIB, but they are definitely still available and there are advantages. (weight and storage, are two advantages).

Our P.O.S Zodiac 12' Air-Floor dingy planes well when everything is pumped up hard. Even with 4 people planing is possible with a big (15hp) motor. But previously we could plane in a similar boat with a 4HP Merc (one person). The length of the hull DOES matter. A longer boat planes easier. A long, light boat planes quite easily with less horsepower. A short heavy boat will be difficult to make plane.

Advantages of a large, air floor, dingy:

• Light weight, you can pull it up the beach, even old folks can with big wheels on it. You'll appreciate that when you try to pull your 2.8mt RIB with a 4 stoke motor and a tank of gas and some "stuff".
• Less power needed.
• Storage: For passages the soft bottom (air floor) dingy can be deflated and rolled up and stuck below, keeping decks clear.

Disadvantages:

• Having to inflate it
• Less than rigid shape makes planing with a load more difficult
• Poor handling in choppy water (no not wetter!)
• Miss-named inflateable, should be "deflateable" They leak!

[Jammer]

Originally Posted by rslifkin

Only for the newer units. Older small Merc outboards aren't rebranded Tohatsus like the current stuff.

So, apropos new cruisers on a budget, I think it is a valid question whether used outboards are worth considering.


Realizing that the markets are local and vary from place to place, it has been my experience that it is difficult to buy a good, used outboard motor in the 10hp-15hp range. In this size range boats outlast the motors (keeping in mind that in the broader, general market, not cruising particularly, these boats are aluminum) and demand is always strong. These engines are good for maybe 2000 hours and they get run out. I bought a new 9.9 in 2021 when things were especially bad because of COVID. It was hard to find new ones let alone used. Used listings are still rare with a few 1970s-1990s engines showing up, mostly Johnson and Evinrude, not something I would want to take on a cruise outside the USA.


On the other hand there are half a dozen 3hp motors on craigslist here on any given day, and they are typically lightly used. People bought them for once-a-year canoeing or duck hunting trips.

[rslifkin]

Good used outboards are definitely a tough thing to find in some areas. Around here, it took a long time to find a good one. I eventually got a rather good deal on a few year old Tohatsu (one of the Nissan branded ones) in very good condition (and that had only seen fresh water). But the majority of what's for sale around here are either long shaft (not suitable for most dinghies), 30 - 50+ years old, or larger. Coastal areas likely have a better market.

[wingssail]

Originally Posted by rslifkin

Only for the newer units. Older small Merc outboards aren't rebranded Tohatsus like the current stuff.

The Tohatsus and Mercurys are made in a factory jointly funded by Tohatsu and Brunswick, parent of Mercury The motors are nearly identical but Mercury is still involved in the engineering of their brand. There are small differences such as the gear shift in some models.

Mercury motors over 40 HP are made elsewhere. Mercury has 16 factories world wide but most are assembly factories. Engineering and casting is largely done in Fond du Lac, Wis. Verado motors, including the 600HP V-12 are made in Fon du Lac.

And Mercury still markets an entire line of 2-stoke motors up to 250hp and the 15hp 2-stroke looks remarkably like the 8-9.9-15HP last manufactured in Fond du Lac prior to 2020. It weighs 77lbs.

Parts for older Mercury motors are still available.

[Adelie]

Originally Posted by Jammer

So, apropos new cruisers on a budget, I think it is a valid question whether used outboards are worth considering.


Realizing that the markets are local and vary from place to place, it has been my experience that it is difficult to buy a good, used outboard motor in the 10hp-15hp range. In this size range boats outlast the motors (keeping in mind that in the broader, general market, not cruising particularly, these boats are aluminum) and demand is always strong. These engines are good for maybe 2000 hours and they get run out. I bought a new 9.9 in 2021 when things were especially bad because of COVID. It was hard to find new ones let alone used. Used listings are still rare with a few 1970s-1990s engines showing up, mostly Johnson and Evinrude, not something I would want to take on a cruise outside the USA.


On the other hand there are half a dozen 3hp motors on craigslist here on any given day, and they are typically lightly used. People bought them for once-a-year canoeing or duck hunting trips.

Part of the reason I started this thread is to figure out what the lowest bar to entry is for new cruisers, especially those starting in the US or Europe where they are going to have to start with a 4-stroke.

My take it that new cruisers can start with an Ultralight RIB pushed by a 9.9hp 4-stroke. This will get a couple on a plane. A year or so along and they are out of the US and Europe and are sure they want to keep going they can upgrade to a 15hp 2-stroke. This minimizes up front costs while maintaining the capability to plane albeit somewhat slower or with less maximum load.

[Adelie]

Originally Posted by wingssail

The Tohatsus and Mercurys are made in a factory jointly funded by Tohatsu and Brunswick, parent of Mercury The motors are nearly identical but Mercury is still involved in the engineering of their brand. There are small differences such as the gear shift in some models.

Mercury motors over 40 HP are made elsewhere. Mercury has 16 factories world wide but most are assembly factories. Engineering and casting is largely done in Fond du Lac, Wis. Verado motors, including the 600HP V-12 are made in Fon du Lac.

And Mercury still markets an entire line of 2-stoke motors up to 250hp and the 15hp 2-stroke looks remarkably like the 8-9.9-15HP last manufactured in Fond du Lac prior to 2020. It weighs 77lbs.

Parts for older Mercury motors are still available.

My understanding is that Tohatsu, Nissan and Mercury outboards in the dinghy sizes are all the same motor with cosmetic differences.

[wingssail]

Originally Posted by Adelie

My understanding is that Tohatsu, Nissan and Mercury outboards in the dinghy sizes are all the same motor with cosmetic differences.

Nissan are no longer sold. Mercury and Tohatsu under 40 hp are the same motor built in a jointly owned factory, Tohatsu Outboard Corporation. Like I mentioned, there are differences, such as the gear shift in the tiller handle in some mercs. Engineering, I believe, is a contribution from both companies. The model line-up is in constant change.

[rslifkin]

Wingssail's description is dead on for the Tohatsu / Mercury thing. And yes, the 2 stroke Mercs they don't sell in the US anymore are not Tohatsus as far as I know. The Nissans (no longer available) are 100% identical to the equivalent Tohatsu save for the paint color and stickers. There are other partnerships in larger sizes, such as Honda building larger outboards for Tohatsu.

[Jammer]

Originally Posted by Adelie

My take it that new cruisers can start with an Ultralight RIB pushed by a 9.9hp 4-stroke. This will get a couple on a plane. A year or so along and they are out of the US and Europe and are sure they want to keep going they can upgrade to a 15hp 2-stroke. This minimizes up front costs while maintaining the capability to plane albeit somewhat slower or with less maximum load.

Realizing that mine is a minority opinion, I believe that a displacement-speed dinghy is a reasonable alternative, especially in the USA. Most of the USA cruising grounds (aside from southern Florida) don't require long dingy rides. CF has a structural bias towards Caribbean and South Pacific cruising. In, say, the Chesapeake, or the Great Lakes, the underwater topography is steeper, anchorages are deep, and long dinghy rides aren't necessary.

[rslifkin]

Originally Posted by Jammer

Realizing that mine is a minority opinion, I believe that a displacement-speed dinghy is a reasonable alternative, especially in the USA. Most of the USA cruising grounds (aside from southern Florida) don't require long dingy rides. CF has a structural bias towards Caribbean and South Pacific cruising. In, say, the Chesapeake, or the Great Lakes, the underwater topography is steeper, anchorages are deep, and long dinghy rides aren't necessary.

Agreed. So far, I've found the faster dinghy to be a convenience, but not a necessity. In many places I wouldn't reasonably get the dinghy on plane anyway, and in other places it saves a few minutes of travel time at most. Most of the times I've had it on plane for more than 3 or 4 minutes have been exploring.

Of course, there are some areas where 1+ mile dinghy rides are a regular occurrence and a faster dinghy is a big advantage If you get a dinghy that can handle more power, there's always the option to get a bigger outboard later if going to areas that need a faster dinghy.

[Adelie]

Originally Posted by Jammer

Realizing that mine is a minority opinion, I believe that a displacement-speed dinghy is a reasonable alternative, especially in the USA. Most of the USA cruising grounds (aside from southern Florida) don't require long dingy rides. CF has a structural bias towards Caribbean and South Pacific cruising. In, say, the Chesapeake, or the Great Lakes, the underwater topography is steeper, anchorages are deep, and long dinghy rides aren't necessary.

My preference is to row or use an electric trolling motor.

However there are plenty of newbies heading off to the Caribbean and Pacific and I want to help them to limit up front costs especially when a certain amount of them won’t like the life and throw in the towel.