Is 6hp outboard enough power?

[osprey877]

I have just bought a new 9' RIB. It is fairly light at 80 lbs and is rated for 10hp.
I would like to power it with a new 4 stroke 6 hp outboard (2 stroke is not available in US/Canada) as this is relatively lightweight to hang off my pushpit and for my wife and I to manhandle. It is also the largest outboard that has a an integral gas tank. I want to avoid the hassle of filling and storing a separate tank, the minimum size of which seems to be about 5 gallons. I currently have an integral tank 2.5hp and fill it from a couple of 1 gallon jerry cans that fit in my vented cockpit storage bin. I am hoping to keep using the same system.
My question is whether or not a 6hp outboard is powerful enough to get the RIB onto a plane at WOT when carrying the 300 odd lbs that constitute my wife and I. The dealer says yes, but I'm hoping someone with actual experience can chime in. Most people seem to use a 9.9, but all seem to agree that is way more powerful than necessary if there's only 2 in the boat, and the 9.9 is considerably heavier than the 6. Will the 6 work, or do I need to bite the bullet and get an 8 or 9.9?l Thanks

[jamhass]

Will the dealer demo the 6 on your dink?

[Panope]

This thread might be helpful:

https://www.cruisersforum.com/forums...rs-256380.html

[osprey877]

Originally Posted by jamhass

Will the dealer demo the 6 on your dink?

Maybe, but I doubt it. They don't seem to have demo models, at least not in the small sizes. Perhaps though they let me return it for a store credit or something if it doesn't work. Anyways, good idea. I am still hoping to get some initial feedback to see if I would just be wasting my time shopping and comparing 6hp engines.

[sailorboy1]

I had a 6 HP outboard in the past and changed to a 9.8. With 2 people in the dink it didn't go any faster and with 1 only 1 it was extra squirrely.

[Plumbean]

I asked this same question a few days ago here: https://www.cruisersforum.com/forums...ml#post3865314


So far nobody has taken it up.


What dinghy are you contemplating?

[wholybee]

It's borderline, it might and might not plane with 2 people. 300 lbs is on the light side of having 2 people, so if the dinghy itself is one that planes easily it should do it. Hull shape matters. A shallow V will plane easier than a deeper V, but a deeper V will have a nicer ride.

Rule of thumb is 4hp per person to plane. 6hp would plane easily with one and have power to spare. You might be able to go with a lower prop pitch for a slower top speed, but be able to plane with two. 8hp would be preferred for 2.

[osprey877]

Originally Posted by Panope

This thread might be helpful:

https://www.cruisersforum.com/forums...rs-256380.html

Yes, thanks. Very helpful.
Seems consensus is that 6hp might work, ….but very dependent on weight of tender, motor and occupants.

[Mirage35]

FWIW

I had a 6 hp Tohatsu on our ultralite 8 foot RIB. It would plane with just me (150 lb soaking wet) on board, but that's it.

[Cheechako]

Originally Posted by osprey877

I have just bought a new 9' RIB. It is fairly light at 80 lbs and is rated for 10hp.
I would like to power it with a new 4 stroke 6 hp outboard (2 stroke is not available in US/Canada) as this is relatively lightweight to hang off my pushpit and for my wife and I to manhandle. It is also the largest outboard that has a an integral gas tank. I want to avoid the hassle of filling and storing a separate tank, the minimum size of which seems to be about 5 gallons. I currently have an integral tank 2.5hp and fill it from a couple of 1 gallon jerry cans that fit in my vented cockpit storage bin. I am hoping to keep using the same system.
My question is whether or not a 6hp outboard is powerful enough to get the RIB onto a plane at WOT when carrying the 300 odd lbs that constitute my wife and I. The dealer says yes, but I'm hoping someone with actual experience can chime in. Most people seem to use a 9.9, but all seem to agree that is way more powerful than necessary if there's only 2 in the boat, and the 9.9 is considerably heavier than the 6. Will the 6 work, or do I need to bite the bullet and get an 8 or 9.9?l Thanks

My gut says NO or best, not well..

A 5 hp planed my 10ft lightweight airfloor inflatable with two people ...... just barely.

My 15HP Yamaha powerd a 10 ft double floor heavy (135#) old RIB fine with 2 + gear.

The 15 hp was too much for a new 9ft RIB after that. Squirrely on a plane but bow up in the air before the plane.

I'm thinking you want the 10 hp for a good 9 ft RIB. 3 gallon tanks are available.

[rslifkin]

Depending on the RIB, a 6hp may or may not plane with 300 lbs. To plane 2 people with a 6hp, you need a fairly easily driven dinghy and the setup has to be just right. Our 12 foot aluminum skiff will plane 400 lbs of people and stuff with a 6hp, but just barely. And it's not fast, top speed is about 9.5 kts with that load (and just barely on plane, can't slow down at all from WOT). Even getting that performance required adding trim tabs to the dinghy for more planing surface and more lift aft.

[Tsuru]

We originally powered our Walker Bay 270 RIB with a 6 HP 4 stroke Yamaha. This boat is heavy (125#) and in spite of being a RIB the plastic rigid bottom has quite a bit of flex. The flexing seems to impact the boat by making it harder to plane.
With just me at 220# the boat planes easily. With my wife on board 320# total weight the boat just won’t jump up on a plane.
I suspect if the boat was a bit lighter or a bit stiffer it would plane with 2.
We recently upgraded to a 9.9 and have plenty of power. Easily planes with 2 and some groceries.
Even with an outboard lift the 9.9 is noticeably more work to get on and off the boat.
In the case of Mercury the 8 hp and 9.9 weight the same #84 so we chose the 9.9.
Good luck with your decision.

[MicHughV]

I've had an 8 hp 2-stroke Yamaha for years. It will put two people on plane in a RIB without any trouble.
Suggest you go from 6 to 8 hp.....the portable fuel tank for those little engines are usually 3 gallons, quite small and can fit right under the engine.
With a portable tank, you can get it filled anywhere, without having to schlep the engine along. A 3 gallon tank is easily carried in one hand.
Most 6 and 8 hp engines are the same, but just with different jets fitted. Typically, the 8 hp will run about 500 rpm more than the 6 to gain the extra 2 hp.
Get the 8. You won't be sorry.

[Plumbean]

Originally Posted by MicHughV

[snip]

...
Most 6 and 8 hp engines are the same, but just with different jets fitted. Typically, the 8 hp will run about 500 rpm more than the 6 to gain the extra 2 hp.
Get the 8. You won't be sorry.

Not correct. The break in design is between 6 and 8. Most of the 4,5 and 6 hp units have the same block with different jets/tuning. The 8 is usually the same as a 9.8, and much heavier. A 6 hp Tohatsu is about 55 lbs. An 8 hp is 82 lbs, as is a 9.8. Then the next grouping is 9.9, 15 and 20.



This is why I am looking at a 6 hp. Much easier to lug around, although I would plan on using an external fuel tank as it has more capacity, is easier to refuel and, at least according to the internet (which is of course always correct) using the internal tank can be more likely to lead to starting problems.

[rslifkin]

With 2 strokes the 6hp model is often a de-rated 8hp. With 4 strokes for most brands, the 6hp is a single cylinder (and available de-rated to 4 or 5hp). The 8 is typically a de-rated 9.8 or 9.9hp 2 cylinder.