Will a new prop help

[williams359]

Hi all. I have a Honwave t30 and a Johnson 2 stroke 9.9hp (2003) On my own or with the kids it flies. With my mate (both 16 stone) it struggles to get out of the hole on the plain. Sometimes it will other times it will not, i think its on the borderline. Once on the plain it flies with the two of use on board. Do you think a different prop will give me that extra 5% to get us on the plain every time. I do not mind loosing some top end speed. The other option are the fins but i can't find ones that bolt on. With opinion split if they work i would be reluctant to start drilling holes in my engine. Bigger engine is not an option. so will a prop with different pitch or a 4 blade one help

Cheers for any help

We do move forward when trying to plain and boat is properly inflated

[Landlockedpirate]

A courser pitch prop may help, but as you have realised you are right on the boarderline for planeing with that amount of weight and reducing the prop pitch may still not be enough. I wuld stick with a 3 blade, yourengine doesnt have the powerto spim a 4 blade very efficiently IMHO.

If you dont fancy a doel fin why not try some trim tabs for the boat instead, these should help a lot.

[williams359]

Thank you for the advice, as i have launching wheels fitted i don't have the space for trim tabs. I would fit the doel fins if i new they would work or if i could get some that do not involve drilling. Its so frustrating as when on the plain with the two of us it flies at 3/4 throttle.

[frankc]

If you are running a 10 1/2" standard prop, you might find the 9" makes the difference for you. We found switching to a 9" stainless to be well worth the money on a 14 ft fiberglass hull.

[Ribochet]

Props are always a compromise between "hole shot" and top end speed.

In your case a finer pitch will definitely help with the scenario of getting you and your mate onto the plane - but you will have a lower top end speed.

A 4 blade prop will be a waste of money

Have you experimented with moving your mate back or altering the setting for the engine trim?

[frankc]

Whoa - I did not realize it was the 9.9 as stated and advised based on the 15. Wish those senior moments would not last so long with me

I believe the 8" pitch prop is standard for the 9.9, so the 9" I recommended is wrong.

[Fenlander]

We've had 3.1/3.4/3.5/3.6m sibs and used 4/8/9.8/15hp motors with loads from one up to two adults with two early teens and a dog plus kit for a day out.

As others have said and you have found with 2 16 stone adults you are on the frustrating edge of plane/no plane. In this circumstance every small factor really adds up such as wind and wave state... but most of all every extra pound you carry makes a huge difference.

Unfortunately the Honwave is quite heavy for its size assuming you have the alloy floor... it's about 25% heavier than a similar Zodiac. Your outboard is about 15lbs heavier than the lightest in class and if your transom wheels are the flip up type that stay on they add a bit.

Doel fins have never really worked for me as they introduce drag with the lift they give so 50-50 benefit/no benefit.

I assume you have the boat right up to pressure and have checked on the gauge after it has been on the water a few minutes? Nothing (apart from your mate) you are carrying that can be left behind? How much fuel do you carry and where is the tank? Where do you both sit and do you try moving about as the planning point is reached to get a balance where it will try and jump away?

If none of the above leads you to an answer I'd get a finer pitch prop. I've swapped props about on similar outfits and the change is very noticeable... even a new standard prop will improve on a very ragged old one. Agree a 4 blade will not help... probably be worse. Also bear in mind there can be a slight difference in blade profile between an original and aftermarket prop which with the knife edge you are on and add to your problems. I would stick to an OE one if you can.

Frankc knows his stuff but I would have thought in the UK your 9.9 might have been a 9.5" pitch as standard.

In any case I would give Steel Developments a mail/call... Home page

They know so much about props and in my experience give honest advice. They would want about £70 for a new prop or £40 if they have a recon one in the pitch you need... their recon is as good as new. They would recon your own for about £35 and I wonder if they could reset the pitch to whatever you decide is needed.

I found this Evinrude prop guide that is of general interest and on page 17 refers to the prop choices for your outboard...

http://www.evinrude.com/content/pdf/...ide_766315.pdf

[williams359]

Thank you for all the great advice it is very much appreciated. The book states its a 9.5 x 10 prop. At around £70 i will give steel developments a shout. I have tried every thing else apart from a diet

[Fenlander]

Yep I agree... £70 is cheaper than swapping boat or engine... and quicker than a diet! Do ask them about OE prop prices vs the standard Solas they usually supply at £70... in my experience the Solas was worse for efficiency and in a marginal performance case it made a difference.

Pitching down so you can always get on the plane but losing ultimate top speed when one up is overall more rewarding for boat use unless totally antisocial.

[frankc]

That foot in my mouth is starting to taste rank, but the old 18 HP used the 10 1/2 cupped and the 15 HP used the 9 1/2 x 10. You can certainly step down in pitch and pull more power out of that 9.9.

Our 15 did not handle the 10" pitch well, so it is no wonder you are loading up your motor.

I see they referred you to a prop chart, but if you have trouble accessing it, there should be one in my garage.

I had run tests on the props in the past with several small boats, but I gave my grandson the data recently and all that is left is a poor memory

[Locozodiac]

Why don't you bump that Evi/Johnson 9.9 to a 15 HP, will need : 15 HP reeed valve assembly, carb and VA gaskets to have have factory converted 15 HP. Before you guys play with prop pitches must know wot rpm numbers with an induction tach, not blindy, as this could over rev or lug engine which is bad music.

Parts may still be available, will have better thrust, hole shot with a 15 than with a 9.9.

Is a T30 a 320 Mt sib ? if so, too much hull drag to overcome fast along weight with a poor 9.9 HP engine.

Happy Boating

[williams359]

i have spoken to the prop people and they have recommended a 9.25x9 instead of the 9.5x10 i have also ordered a meter to check what revs i will be running to make sure i do not ruin the engine. I will let you know how i get one.

[Locozodiac]

Go for a wot spin with you alone and light loaded sib on a flat calm no wind waters and stay with the prop pitch that delivers full or near full wot factory rpm stated for that engine. Will have good hole shot and top speeed.

Happy Boating

[williams359]

I went for a Stainless Steel prop in the end, which was a lot of money but i hope the right choice. so i have gone from a 9.5x10 to a 9.25x9. I went out today to check the RPM. The book has it up to 6000rpm, with me on my own WOT was 5800rpm. Hard to say if its any better as i was on my own and it always flew on my own. I will report back once i have been out with my mate.

[Locozodiac]

With previous prop, what were the numbers at wot with you alone ? stay witht the one that delivers the nearest 6 K at wot, bear in mind that as soon you start adding weight, rpm will drop accordingly.

Happy Boating

[williams359]

The results are in and they are good. With the old prop is was a right pain trying trying to get the boat to plain with the two of us on board. Im pleased to report the new prop has made the difference. I have lost a little top end but that was to be expected. The main thing is i can now get it to plane every time with my mate and i. What i did not expect i can also get it to plain with the me the wife and my two girls on board. Thats a least two stone more than just me an my mate. All within the recommended RPM, even with just me on a calm day