Getting more power from outboard 4 strokes

[geem]

Just opened up my DF4 to lube the throttle cable and noticed a "4" stamped on the cable clamp that doubles as a throttled restrictor. By bending it back to allow full throttle, it appears to have gained 300 to 400 more RPM and I can now get on the plane 2-up and I clock-in at over 100kg so 3-up a distinct possibility! I have the Suzuki 4 mounted on a generic 3.2m vinyl RIB.

We had probably the lightest air deck dink with a 6hp fourstroke. It would plane with two up (135kg) and minimal shopping. It needed a large planing plate to help it on to the plane. This was a 2.8m dink. I cannot see you planing 3up, unless they are kids, with 6hp. We now have a 2.8m rib with 15hp 2stroke that can plane with four light adults or three chunkies. We couldnt do this with our 9.8hp 2stroke even with large planing plate fitted to the engine.

 

[lw395]

....We couldnt do this with our 9.8hp 2stroke even with large planing plate fitted to the engine.

Have you asked Tranona if you might have been over-propped?

 

[yotter]

I have a 6HP mariner. 6HP seems optimum since the same engine weight as a 4 or a 5HP. To get 8HP or more, you need 2 go to twin cylinder and an extra 10Kg:-(. Our 2.8m fastroller airdeck zodiac easily planes 1 up and sometimes planes 2 up with a following wind on a good day. On the basis that most 4/5/6HP engines are the same weight, the OP could consider selling/trading in for a 6, as already suggested.
Angus

 

[ip485]

I cant imagine you will get almost anything to plane with 6HP. I have a Ribeye because it is about the lightest Rib with hard bottom I could find. Its around 50KG. I also have a 15HP 2 stroke because it offers better power to weight ratio than a 4 stroke and can get the Rib on the plane 2 up easily, but not with three adults (with three its just not quite powerful enough). To be fair with three adults all around 10 stone I am guessing it would just do the job. I am thinking of a 20HP engine which I reckon should provide planing performance with even four adults, but it will be interesting to see if it planes with three but then still not quite enough for four. Maybe a rule of thumb is 5HP per adult to plane!?

 

[alanejread]

No need to trade-in as your 4 may already be a 6, albeit with just a throttle restrictor. Can anyone confirm this?

 

[rotrax]

The 4-5and 6 hp Suzuki's are the same basic engine-I was told this by the Plymouth Suzuki agent.

The 4hp is restricted by carb butterfly movement. A new throttle plate stamped "5" will give the extra power, or just bend it to allow full 'ole. DONT let the butterfly go past the horizontal!

The 6 hp has a bigger carb.

They are excellent engines, very reliable.

I have one for sale almost unused and converted to 5 hp if anyone is interested, as well as an Evinrude 6 hp two stroke twin with low hours.

PM me fo info.

 

[lw395]

I used to have a Mariner 3.3 which would plane a light 12ft GRP dinghy one-up.
But it wouldn't make my Bombard plane without wave assistance.

Some of these engines have to be revving a lot to make their full power. Some don't make very good torque at lower rpm. If the dinghy is too short and slow in displacement mode they will never get there.
It's quite hard to guess what rpm a small outboard is doing which makes it hard to know how much power we are getting out of our '5hp' egg beater.

 

[GrahamM376]

Re: Ditch the 4 stroke

We had a suzuki 6hp and it just couldn't get the revs to plane a 3.2M dinghy with 2 people we chaned the prop still no luck - some friends had the same engine and couldn't plane 2 up with an Avon 2.8M rib we ditched the 4 stroke and bought a Yamaha 8hp 2-stroke - wonder of wonders it planes the 3.2m dinghy with 2 up.

Same experience and not too reliable either. Ditched ours for larger second hand 2 stroke. According to the dealer we purchased DF6 from the difference between the models was rev limiting electronic module and carb jets.

 

[seumask]

Get a light aluminium bottomed RIB. A good friend has a 3.5M AB used as a tender to his large AL yacht. It's powered by a 2 stroke Yamaha 9.9 uprated to 15 hp and it planes happily with 3 adults in it , it's a weapon with 1 adult in it. Longer , Lighter and stiff all seem to make this one go very well.

 

[TQA]

Dolphin fins really help you to get up on the plane. But even with fins you are pretty unlikely to get 3 people up on the plane with 6 hp. You need a minimum of 8 hp and a lightweight dink . Even then it will be marginal.

Where I hang out Yam 15 and Tohatsu 18 obs are the weapon of choice [ 2 strokes of course. ]. Plane 3 people with shopping into wind.

 

[geem]

Get a light aluminium bottomed RIB. A good friend has a 3.5M AB used as a tender to his large AL yacht. It's powered by a 2 stroke Yamaha 9.9 uprated to 15 hp and it planes happily with 3 adults in it , it's a weapon with 1 adult in it. Longer , Lighter and stiff all seem to make this one go very well.

I find the very light AB aluminium ribs tippy as hell. We use a Caribe 9ft lite. It weighs 54kg plus the 35kg two stroke 15hp Yamaha Enduro. Not exactly light but with a large planing plate it planes quickly, will carry three large adults on the plane at high speed without a problem. I picked up some new anchor chain with it last season. 60m of 10mm chain weighing 122kg plus my 75kg weight. I took it 1.5miles at full speed throttle on the plane back to the boat with no problem. Our rib is our car. It does everything we want of it. We dont drag it up the beach anymore but anchor it in the shallows instead. We carry a couple of anchors at times so we drop one as we approach the beach and take one on to the beach as well. This way we can pull it in the the beach to get back in without having to wade out in to deep water. This wouldnt work for tidal waters or British mud!

 

[ip485]

My Rib is 3.10 m and as I mentioned earlier with a 15HP two stroke. The Rib weighs 55KG. It is interesting others expereince that this shoud readily plane with 3 up and shopping. As I mentioned earlier, with 2 up I find it planes easily. Three up and even with all the weight well forward I can feel that it will not quite get on the plane. It is almost there but not quite. Maybe a larger planing plate would do the job, it would seem this makes a big difference.

 

[geem]

My Rib is 3.10 m and as I mentioned earlier with a 15HP two stroke. The Rib weighs 55KG. It is interesting others expereince that this shoud readily plane with 3 up and shopping. As I mentioned earlier, with 2 up I find it planes easily. Three up and even with all the weight well forward I can feel that it will not quite get on the plane. It is almost there but not quite. Maybe a larger planing plate would do the job, it would seem this makes a big difference.

Our planing plate is home made. Design given to me by a very well respected skiff designer. They are BIG. The difference to performance is incredible. I took mine off last year to paint it so was running around for a couple of days without it. The rib was terrible by comparison. Hard to get on the plane, fast to drop off it, skittish and needed more throttle.

 

[GrahamM376]

My Rib is 3.10 m and as I mentioned earlier with a 15HP two stroke. The Rib weighs 55KG. It is interesting others expereince that this shoud readily plane with 3 up and shopping. As I mentioned earlier, with 2 up I find it planes easily. Three up and even with all the weight well forward I can feel that it will not quite get on the plane. It is almost there but not quite. Maybe a larger planing plate would do the job, it would seem this makes a big difference.

Something's wrong, maybe prop pitch or engine angle? Our ply floor inflatable keel 2.9 weighs the same at 55kgs and will just plane 3 up with 9.8 2 stroke (without plates) if one sits on the bow. Your rib should be much quicker.