Which RIB & engine?

[SY Kelpie]

We're thinking that we should upgrade to a RIB once we move aboard the boat. I've read different things about what to expect in the way of performance, and what size of engine is necessary, etc.

Ideally we would like to keep the overall cost and weight down, buying secondhand if possible. I'd love to be able to keep the engine size manageable, say a 6hp, or a 10hp as an absolute maximum. But I've been told that using an engine that is too small will result in the boat not getting up on the plane, and using more fuel as well.

So- what we need is something no more than 3m long, preferably with Hypalon tubes, and with enough performance to plane with three smallish people aboard... let's call it an all up crew weight of no more than 200kg.

What combinations of RIB and engine are going to achieve this?

[flyingfin]

The typical RIB is heavy, you cannot lift onto deck without good davits or 4 strong persons. Two people can easily lift an inflatable with an inflatable keel and floor boards onto the deck from the water. One person can lift a 4hp or 6hp motor. A strong person can lift a 9.9 or 15hp for a short distance. I need an engine hoist to lift my 25hp off the RIB when the RIB is on its trailer.

I will not cruise offshore with an inflatable in tow, either RIB or regular inflatable. Too many problems to list here.

Suggest you borrow one and figure out what your intended daily use and storage options are.

[leftbrainstuff]

We sold our old Avon rib and 15hp two stroke.

We now have a Portland Pudgy and a 4/1/2 hp two stroke and 2 hp electric motor. No more tubes to worry about.

I can now manage the motors without a crane and the pudgy is easily manageable with two. It even has hand holds and a wheel built in.

[dksail]

We have an 8'-10" fiberglass RIB (85 lbs) with a new Tohatsu 6hp 4 stroke. With a 200 lb load (1 person and gas) it can easily plane. With a 320 lb load (2 people and gas) it struggles but can get there in calm water with no head wind. If planing is a must, go with a 10 hp.

[SY Kelpie]

Originally Posted by dksail

We have an 8'-10" fiberglass RIB (85 lbs) with a new Tohatsu 6hp 4 stroke. With a 200 lb load (1 person and gas) it can easily plane. With a 320 lb load (2 people and gas) it struggles but can get there in calm water with no head wind. If planing is a must, go with a 10 hp.

Thanks, that's great information.
I wonder how much the design of the RIB affects the hp needed to plane- or is it really all down to weight?

We are looking into RIBs of the same sort of weight as yours, up to around 40kg plus engine. The Tohatsu 2 stroke 9.8 seems like a great engine from what I've read, at under 30kg.

[Fixer]

After looking long and hard, we found the Whaly - no more tubes and no worry about barnacles on pillings. Just be mindful of bumping the mother ship...
https://www.whalyboatsusa.com/product-page/model-270

[ranger58sb]

Originally Posted by SY Kelpie

What combinations of RIB and engine are going to achieve this?

Consider the question as within your whole proposed whole system of vessel, motor, weight (fuel tank? battery? etc.), transport system (davit? tow?), purpose (speed required? hauling groceries or bicycles?), does transport require dismounting the motor, etc.

-Chris

[Kenomac]

Three people up on a plane usually means at least 15hp minimum and a hard bottom rib.

[SY Kelpie]

Originally Posted by ranger42c

Consider the question as within your whole proposed whole system of vessel, motor, weight (fuel tank? battery? etc.), transport system (davit? tow?), purpose (speed required? hauling groceries or bicycles?), does transport require dismounting the motor, etc.

-Chris

39ft centre cockpit sailing boat. Plan is to store the dinghy on deck for longer passages, but in davits with motor attached for overnight and day sails. We generally avoid towing dinghies unless on a very short passage.

I would like a dinghy that can plane for a number of reasons- being significantly faster than the mothership allows us to scout ahead when navigating tricky anchorages, and extends our exploration range when going ashore. It will also make it easier and less tedious when having to pop ashore for admin or supplies.
Planing is, I am led to believe, more economical and drier than travelling at displacement speeds.
A powerful dinghy engine will also be a good thing to have when laying a kedge anchor, or if we have problems with the yacht's own engine.

We're not at all interested in towing wakeboards and we're not speed freaks- so no zooming around just for the sake of it. And we can live with travelling slowly when carrying bigger loads.

[SY Kelpie]

Originally Posted by Kenomac

Three people up on a plane usually means at least 15hp minimum and a hard bottom rib.

A RIB (i.e. hard bottom) is a given. I've heard of people getting small lightweight RIBs planing with much smaller engines than that. Most of the RIBs I've been looking at aren't rated for anything over 10hp anyway.
It would be great to hear specific real world examples of RIB/engine combos that can plane with three people aboard, using smaller engines.

[sailorboy1]

Originally Posted by SY Kelpie

We're thinking that we should upgrade to a RIB once we move aboard the boat. I've read different things about what to expect in the way of performance, and what size of engine is necessary, etc.

Ideally we would like to keep the overall cost and weight down, buying secondhand if possible. I'd love to be able to keep the engine size manageable, say a 6hp, or a 10hp as an absolute maximum. But I've been told that using an engine that is too small will result in the boat not getting up on the plane, and using more fuel as well.

So- what we need is something no more than 3m long, preferably with Hypalon tubes, and with enough performance to plane with three smallish people aboard... let's call it an all up crew weight of no more than 200kg.

What combinations of RIB and engine are going to achieve this?

I have an inflatable bottom dinghy and a 6 HP outboard. With one person it planes and gets so squirrely that it is almost hard to control unless you slow down. with 2 people it change of slow and other cruisers past us like wwe aren't moving.

I was thinking I needed a bigger outboard. But a few months ago a cruiser flew by us and they had the same exact outboard, but a hard bottom dinghy. So when my dinghy finishes dying I'm going to go to a hard bottom with the 6 HP. If I later need to upgrade the outboard I will then know it.

So my recommendation is a hard bottom RIB with a smallest motor of 6-7.5HP and see if that does it for you. Later if you decide you need get a larger outboard you can sell the other and not be out that much in the bigger picture. But if the smaller outboard is enough you saved a lot by not buying and fighting with the larger outboard.

[Lionelsole]

On the theme of this thread.
I have recently changed from a flat bottomed inflatable to a baby rib (highfield ul260, which, at 68 lbs, actually is lighter)
I have a 4 hp mercury, which was plenty for the inflatable. With the RIB, it planes nicely 1 up but not with 2. The boat is only rated for 6 hp. Does anyone have this specific combination? Should I look to trade-up my motor or would I just burn more fuel and still not plane?

[SY Kelpie]

Originally Posted by Lionelsole

On the theme of this thread.
I have recently changed from a flat bottomed inflatable to a baby rib (highfield ul260, which, at 68 lbs, actually is lighter)
I have a 4 hp mercury, which was plenty for the inflatable. With the RIB, it planes nicely 1 up but not with 2. The boat is only rated for 6 hp. Does anyone have this specific combination? Should I look to trade-up my motor or would I just burn more fuel and still not plane?

That's the kind of setup I'm talking about- <3m RIB weighing around 35kg (80lbs) and as small an engine as practical. I haven't heard anybody suggest that 4hp would get anything on the plane, tbh... the smallest I've heard of was 6hp. But I guess it comes down to weight?

[a64pilot]

A whole lot of dinghy performance, especially small motors is how it’s propped, before I popped for a bigger motor I’d get a cheap inductive tachometer and see what my RPM is compared to what it’s supposed to be, if your more than 500 RPM lower than optimum, then you need a flatter prop.

Just as a comparison, my 20 HP came with a 10” prop, it would literally jump onto plane and about the the time it got going fast, it would hit the rev limiter, so I bought a 12” prop, then it would only plane with two people if we were way forward and pretty flat water and it would just barely crawl onto plane.
Of course we ended up with an 11” prop.

We now have a different dinghy that is a much slower boat, and likely the original 10” prop would be best for it.

[Lowcountry]

My last RIB was a 2014 10' Mercury with a GRP bottom and a 9.8hp Tohatsu. It would plane with thee adults, but not with four. Weight of that dinghy was about 112lbs if I recall correctly. Outboard was probably in the 65lb range. It was a good setup, and would really haul you know what with only one or two people in it. My next setup, which will be for a smaller sail boat, will be an 8' aluminium-hulled RIB weighing less than 90lbs and a 6hp outboard. Not sure if that will get two people up on plane yet, but I know it will get one up.