Honwave T38 planing like buckaroo

[Kong]

Hi all please help

I’m running a t38 honwave with a mariner 15hp short shaft 2 stroke and every time I try and get it to plane it jerks around and the engine revs up and down.

Boat had 2 adults, 1 child and a fair amounit of gear spread evenly. Air floor was topped up to 0.8 bar after we’d been on the sea for a while.

I had a browse of the forum and seen about cavitation and ventilation which I don’t fully understand. The cavitation plate is approx 1” below the floor and approx level with the little keel thing that runs the length of the boat.

I tried to video the problem, it’s worse than it looks. The engine is making lot of noise but not really making much progress!

https://youtu.be/lOwBYXvXobw

This is really annoying, can anyone help please? ��

[goearth]

Not easy to see from the video, but some things to check are:
1. The trim of the engine. Try small adjustments of the trim
2. Have you got a short shaft or a long shaft engine? (see article below)
3 Try adjusting the weight distribution i.e. moving people about.
4. I assume (from your description) that the engine itself is OK - just the boat movements causing the rev changes
5. Keep the pressure up on the airdeck. Test with slightly different pressures; and see if the pressures drops after a while. (Cool water can lower the pressure)

Adjustments should be done a bit at a time and keep a record of what works

Also, see the thread (if you've not seen this one yet) at: http://www.rib.net/forum/f50/honwave...ity-63469.html .
and

https://stufishing.com/testing-honda...t38-outboards/ (the issue is mentioned about halfway down).

Conclusion - does seem to be a common issue with the Honwave - but making the suggested adjustments / tests might minimise the issue.

Hope this helps.

[Yabadabadoo]

My first thoughts:

Prop slip - unlikely but if the prop has hit a rock the hub could be spinning

Cavitation caused by air pocket, are you correctly inflated on all tubes and floor? Inflatables can develop an air pocket if weight is not spread right or under pressure

Assuming it's definitely a short shaft outboard height should be correct for Honwave, is it sitting flush to the transom.

What trim setting is the outboard at 1, 2 or 3

[A1an]

Ive got a T38 and if the trim or airdeck aint right its a handful. Get it right and they are great fun.


The airdeck needs to be as hard as a goats knee.


Id try bringing that engine in another hole

[goearth]

Hi A1an. How many bar is a boats knee :-) ?

[A1an]

Originally Posted by goearth

Hi A1an. How many bar is a boats knee :-) ?

0.8bar and a little bit more

I use a Bravo pump to top up when its dunked in the water.

If its a smidge under pressure then its no better than riding an inner tube

[Pikey Dave]

Originally Posted by goearth

Hi A1an. How many bar is a boats knee :-) ?

About 1000 billybaa

[Mikefule]

Originally Posted by Kong

I had a browse of the forum and seen about cavitation and ventilation which I don’t fully understand. The cavitation plate is approx 1” below the floor and approx level with the little keel thing that runs the length of the boat.

A lot of people incorrectly use cavitation and ventilation interchangeably. However, they are not the same thing.

Ventilation is a common problem. It is quite simply the propellor drawing air in. The propellor is then spinning in a mixture of water and air bubbles. The propellor spins faster than it should but produces less thrust. It is a Bad Thing. The air may be drawn in because the engine is set too high on the transom, or because it is angled incorrectly (trimmed too high or too low), or because the shape of the hull is collecting air underneath and directing it into the engine.

If the propellor ventilates and loses thrust, the boat will slow down and this may stop the ventilation. The boat then speeds up and the ventilation starts again. The cycle continues until something is changed: most likely, throttling back a bit until you can find a better solution.

The three easiest things to try are (1) Pumping the boat and floor up a bit harder (2) adjusting the trim of the engine, one hole at a time, and seeing what happens, and (3) trimming the boat by moving the weight of crew and equipment forward.

Don't forget that if you pump the boat up to the right pressure on land, in direct sun, then drop it into cold water, the air inside it will cool and contract and the pressure will drop. Always be prepared to add more air once the hull has cooled.

Cavitation is a bit more technical and I can only offer a simplistic explanation. Think of a spinning propellor as a set of little wings passing rapidly through the water. Each wing produces high pressure on one side and low pressure on the other, similar to how a wing produces lift. The extreme low pressure causes air/gasses dissolved in the water to form bubbles (a bit like how taking the top off a lemonade bottle reduces the pressure and causes bubbles to form) and these bubbles can make the propellor less efficient and even damage the surface of the metal.

I do not think that cavitation is likely to be a serious problem for a small to medium engine such as yours in normal use. Your problem is more likely to be ventilation.

Other possibilities include the propellor slipping, or a more serious problem with the engine, but go for the simple stuff first, because outboards are pretty robust.

Good luck.