Honwave T32 + 9.8hp Tohatsu 4st + 265kg payload = 5 knots?

[ben1979]

Hi,

New to the forum and after some advice please. Just purchased a new Honwave T32 and first used a 4hp Johnson 2 stroke which was smokey and slow, so just replaced with a Tohatsu 9.8hp 4 stroke. Overall a big improvement but still seems slow. Now I should say that our first testing involved 3 adults and two kids - an estimated total payload of 265kg not including outboard, which is a lot. Our max speed was 5 knots (~6mph) and I was expecting a bit more? Realistically there will always be me, my wife and two kids (200kg payload) so it may be that this limits the speed and a smaller engine would proide the same speed but less weight?

We are using the T32 as a 'play' boat for camping, days out, etc. but also as a tender for our sailboat. I have no experience of inflatables so maybe I am expecting too much with our payload?

Any advice greatly appreciated.

Ben

[Martin]

Welcome aboard Ben.
The tohatsu 9.8 is a great power to weight outboard, tohatsu managing to squeeze masses of power out of where others call it a draw at 8hp. Problem being with that outboard is the severe lack of cc for the Hp.. the old saying of theirs no replacement for displacement kinda shows it’s worth here..
the 9.8 coming in at around 209cc and the 9.9 coming in at 333cc
All that said, I do think you should be doing a lot better than you are, did you check the floor pressure of the T32 once it had been in the water a short while ?

Have you tried adjusting the trim and moving your passengers about a little ?

It would be interesting to know what sort of rpm you’re hitting at wot.

Martin

[PeterM]

With 265kg on board I just don't think you'll ever be able to get it any quicker than 5knts.. with 200 I feel you'll still struggle a fair bit unfortunately:(

Is just not enough power to get to going at those weights.

[ChrisParish]

Speaking as someone who weighs about half of that in their own, I can confirm that with 250kg on board you will not get onto the plane with 9.9hp so 5knots is the best you can hope for.

Our 3.2m zodiac with a 9.9 struggles to plane with 200kg in (and that’s with an old school Johnson 9.9 2 stroke which is a pokey engine). Add an extra 50kg and it would deffo not manage it.

You need more HP and ideally more wetted area (larger boat planes more easily with the same weight in it). The T38 with 9.9hp will plane with 200kg in it without any problem, but 250kg would be pushing it.

Sorry.

On the other hand the T38 with 20hp planes easily with 300kg in it.

[ben1979]

Thank you for the replies, I had been thinking the same thing. So if the payload is always around 200kg and therefore the best we can hope for is 4-5 knts, what is the minimum hp outboard to provide that speed? Would something like the Torqeedo 1103 be enough? The dinghy + outboard must also double as a tender for our sailboat so lifting 40kg on and off regularly for just 5 knts probably isn't worth it.

[ChrisParish]

Practically anything with get you to 4 knots. You are limited more by the load than the HP.

[Martin]

lifting 40kg on and off regularly for just 5 knts probably isn't worth it.

Hang on here, I think maybe thoughts are maybe running away from facts.. ?
Or I’m maybe reading it wrong!

When you say lifting 40kg on and off, are you referring to a 40kg outboard ?

That 3.2ie will far exceed 4-5 knots with the correct outboard on, it’s more a case of whether you want more, able to manage a larger outboard....
Your current 9.8 is no match for a 9.9/15/20hp manufactured at 42-44kg by tohatsu or Suzuki.

Personally imo, if you’re wanting to stick with the 9.8hp, I’d be putting a tach on it and getting a WOT- rpm reading at your loaded weight

Martin

[ChrisParish]

Personally imo, if you’re wanting to stick with the 9.8hp, I’d be putting a tach on it and getting a WOT- rpm reading at your loaded weight

while I agree that getting a tacho on it will give you a better idea of the load the engine is under, my experience of carrying large weights leads me to suspect that you would wind up having to take a lot of pitch off to get the revs up and even then planing will be difficult, if not impossible with that payload.
I know that @Martin is an optimist, but he also weighs sod-all.

[harrison]

With that sort of payload any of the lightweight smaller 200cc 9.8hp motors are not going to get the boat planing. Whilst 5 knots does seem rather slow, it’s probably about the max displacement speed for the hull until there’s enough grunt to climb out the hole. In practice a 4/5/6hp will more than likely push you along at the same speed. In fact our tiny 3.5 aux will push our 5m rib along at the hulls max displacement speed.

Worth checking inflation pressure, trim, depth of av plate, prop size and revs at wot etc. to make sure nothing’s amiss.

To be honest, if you want any chance of getting on the plane with that kind of load, then I reckon you’ll need one of the 15hp efi motors, which are around 43/44kg. If content at displacement speeds then a 6hp should be fine and weigh around 26kg.

[Martin]

I’ve seen the T32ie with that sort of weight in it and run alongside it, difference being the motor size was a 9.9hp.
I wouldn’t be giving up so easy if it was mine, I’ll bet you’re a bubble off getting over the hump!

As I said earlier, get that pressure correct, try different trims and get a tach on it.
It might be a weedy 200cc but that twin should have enough grunt in a decent V floor sib to get it up and over, even if you’ve got to rock the boat

Martin