Planing Dinghy: Hp vs Dinghy type vs #Passengers

[Mike OReilly]

Originally Posted by Adelie

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.

Not sure if I've already said this, but my 3.5 hp Tohatsu easily planes my Portabote with one (fat) adult in it. And will plane with two adults in calm conditions. In all cases, it moves the Bote along quite fast and efficiently.

I think this is because the Portabote is relatively light, but also has an efficient hull design. Given this, I think that tender choice is at least as important, if not more so, when looking at efficient engine/dinghy decisions. A big engine is not needed for an efficient hull.

[Adelie]

You have mentioned it way back on Pg 1 or 2. I recall that you are the only folding boat data.

[Mike OReilly]

Originally Posted by Adelie

You have mentioned it way back on Pg 1 or 2. I recall that you are the only folding boat data.

Thought I might have... Did I mention the PB also rows well, and moves easily with an electric trolling motor .

[wingssail]

Originally Posted by Adelie

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.

What, exactly, is an ultralight RIB?

[rslifkin]

Originally Posted by wingssail

What, exactly, is an ultralight RIB?

One with no double floor or anything else heavy. And possibly aluminum instead of fiberglass. The lightest 10 foot RIBs are solidly under 100 lbs, while the heavy ones with double floors, etc. are 130+. And if you get into the console ones, they're even heavier.

[Jammer]

Originally Posted by wingssail

What, exactly, is an ultralight RIB?

Usually an aluminum (rather than fiberglass) RIB with a single-layer hull and no sole/floor and few if any interior fitments. In contrast, some manufacturers of RIBs in the 2.9-3.3m size range offer a two-layer hull that includes a flatter sole above the V-shaped bottom. Usually these include a modest bow locker for fuel, and allow for the fuel line to go through the hull where it is out of the way.


Then there are RIBs with steering consoles. PT Barnum would be proud.

[wingssail]

Originally Posted by Mike OReilly

Not sure if I've already said this, but my 3.5 hp Tohatsu easily planes my Portabote with one (fat) adult in it. And will plane with two adults in calm conditions. In all cases, it moves the Bote along quite fast and efficiently.

I think this is because the Portabote is relatively light, but also has an efficient hull design. Given this, I think that tender choice is at least as important, if not more so, when looking at efficient engine/dinghy decisions. A big engine is not needed for an efficient hull.

You are absolutely right about the Portabote. It is long and flat and pretty light. It's an excellent shape for planing with a small motor. No rib or inflatable can match it for efficiency. Pretty? No. Efficient? Yes.

I can't put it below and I worry about how it handles rough water, being sort of flexible and all.

But don't accept that yours' is an unusual choice. Every year there are cruisers coming through here with Portabotes. The problem is that cruisers are sheep. They follow the crowd. RIB's are heavy, expensive, hard to stow, and require a lot of horsepower, but everyone has one, so that's what everyone gets. No thinking outside the box.

[Mike OReilly]

Originally Posted by wingssail

You are absolutely right about the Portabote. It is long and flat and pretty light. It's an excellent shape for planing with a small motor. No rib or inflatable can match it for efficiency. Pretty? No. Efficient? Yes.

I can't put it below and I worry about how it handles rough water, being sort of flexible and all.

But don't accept that yours' is an unusual choice. Every year there are cruisers coming through here with Portabotes. The problem is that cruisers are sheep. They follow the crowd. RIB's are heavy, expensive, hard to stow, and require a lot of horsepower, but everyone has one, so that's what everyone gets. No thinking outside the box.

Thanks Wing. If my time on CF has taught me anything, it's that I'm often "outside the box" on many cruising considerations .

Like others of my choices, I recognize they're not for everyone. A Portabote is somewhat different from other dinghies, therefore (as you know) it can't be used in exactly the same way as an inflatable -- at least not in all situations. So it does require a little, as you say, out-of-the-box thinking.

But if you're looking for an dink that moves well under both power and oar, is pretty inexpensive (especially considering the small motor than is needed), is versatile, safe and damn-near indestructible, it's hard to see a better option out there.

The fact that it is considered "ugly" is a bonus in that it's rarely the target for thieves.

[Jammer]

Originally Posted by wingssail

RIB's are heavy, expensive, hard to stow, and require a lot of horsepower, but everyone has one, so that's what everyone gets. No thinking outside the box.

I will point out that I am using a 10' nesting dinghy that I built last winter. It doesn't plane. It rows well, and I see it as useful up to a mile or so away from shore under oar, somewhat further with the 3hp motor. The absence of commercial production of boats like this makes it an option unavailable to most.

[donradcliffe]

It isn't just how many people your dinghy can plane, or how fast it can go.

How many people does it take to carry it up the beach?

How stable is it--can you climb in from one side without it tipping and filling?

How many people does it take to put the motor on and the dinghy in the water?

We had a Swift 3.1 aluminum RIB, 104 lbs. With the 28 lb 3.hp tohatsu two stroke, we could carry it with 2 people, and I could assemble and launch it myself.. We used that combination 95% of the time.

If we wanted to go scuba diving, or had 2 guests, out came the 18 hp tohatsu. It would plane 4, and I remember taking the GPS when I was breaking it in and it topped out at 25.5 knots with just me on board. If we needed to pull it up a beach we had a large set of wheels, but they were a PITA.

[wingssail]

Originally Posted by Jammer

I will point out that I am using a 10' nesting dinghy that I built last winter. It doesn't plane. It rows well, and I see it as useful up to a mile or so away from shore under oar, somewhat further with the 3hp motor. The absence of commercial production of boats like this makes it an option unavailable to most.

Good on you!

[sailorboy1]

My experience says it is the RIB that determines if you will plane more than the outboard. I am on my fourth RIB and third outboard and here is how it has been for me:

RIB #1 with 2HP - didn't plane no matter what

RIB #1 with 6HP - planed with 1 person, didn't with 2.

RIB #2 with 6HP - planed if only one person was in it. Didn't plane with 2 people in it. If only 1 person and planing was hard to steer as it always wanted to turn

RIB #2 with a 9.8HP - still didn't plane with 2 people. Planed a LOT with 1 person but was even harder to steer now. Wasn't any faster with 2 people in it than the it was with the 6HP

RIB #3 with 9.8 HP - planes now with 2 people. Planes just looking at it and I worry about the outboard as the transom is so low. Planes now with 2 people and seems to like this best

[Tupaia]

Originally Posted by wingssail

What, exactly, is an ultralight RIB?

We have a 3.1 m ali rib with a removable collar made by Force 4 in NZ (no longer in business) It weighs in at 34kg (75lbs) and with a 9.8hp Tohatsu 2 stroke (26kg/57lbs) 1/2 tank of fuel another 10kg (22lbs) all up weight is 70kg (155lbs) It will plane with 2 up with full dive sets and can be hauled up the beach (not with dive gear in it) very easily.


Our spare dinghy is a Tinker Fold Up Rib which at only 23kg/50lbs plus a 4hp 2 stroke makes for quick and easy extraction after a surf landing on a beach.


Depends where you are and what you are doing but the key to success is a lightweight motor. A lightweight setup does have the disadvantage of being a little twitchy/bouncy on the water and can be wetter than a big heavy rib.

[Dallasron]

This thread has been around awhile

Jammer: FYI The tohatsu 9.8 weighs in at 81 lbs. The 9.9 is 96lbs. The 9.9 is the same block as the 15 and 20hp models and they all weigh the same.

While there are those who want the minimum, I have always wanted as much as I can handle in size, hp, and weight. My logic:
I may want to go upriver to a restaurant or bar and possible we have another couple with us.
If the weather starts to get iffy I want something to get me back to the boat quickly.
In a pinch my dingy can maneuver the mothership.
I dont want to have to run WOT to make good speed.

For these reasons and they are just my own,,I have a WM350 tender with a 20hp tohatsu pull start paired with a 380. I have an engine davit with a 6 way to pull it up and hang it on the rails.

[Tupaia]

Originally Posted by Dallasron

This thread has been around awhile

Jammer: FYI The tohatsu 9.8 weighs in at 81 lbs. The 9.9 is 96lbs. The 9.9 is the same block as the 15 and 20hp models and they all weigh the same.

Tohatsu 9.8 "4 stroke" 81lbs
Tohatsu 9.8 "2 stroke" 57lbs
https://www.tohatsu.com/marine/int/outboards/M9.8B.html



As always it is vicious circle, more weight needs more power adds more weight and so on. Everyone has to compromise on what is effective for their use circumstances.