Aeration or prop bush slipping?

[Searider]

Afternoon All,

Let the kids loose in the SIB yesterday. Avon RAB315 with Yamaha 4hp 4 stroke.

All seems to run ok but they report what sounds like either the prop ventilating or the prop bush slipping when they are planing. (Two 12 year old boys who each weigh less than a crisp packet!)

I had a short go in it and it seemed OK although the slatted floor does appear to have "waves" travelling along it.

Would increasing the pressure in the inflatable sausage under the floor improve things?
Should I pump the tubes up harder?
Has anyone had a Yamaha 4hp prop bush slip?

Cheers

Duncan

[Downhilldai]

Waves under the floor are a normal feature of these boats.
Difficult to diagnose the engine issue. The pressure of the inflatable keel won't have a significant bearing.
Is there a bush on the Yam F4 or a shear pin? If the latter, then it won't slip.

[Locozodiac]

A slatted floor sib performs badly even top inflated, it's the nature of that beast. Other down issue is that generates excessive water drag undel floor if not counting with a built inflatable keel.

Engine must be trimmed to be perpendicular to water level, check. You could have a near spun prop, prop is beginning to slip inside prop shaft. Will need to perform the prop hub test or get someone else same model prop and test.

Happy Boating

[willk]

I wonder if it's just the different trim. The kids won't have the same effect of burying the back of the SIB that you do. They may just be catching some air?

[Searider]

Thanks all.

Prop does have a bush - I took it off last night and checked. The bush doesn't look chewed up.
Doesn't do it when the boat is heavily loaded.

Engine trimmed correctly I think.

Never had a prop hub tested - the few that have spun have been obvious.

Will experiment with moving weight around and see what happens.

Cheers

Duncan

[gotchiguy]

Originally Posted by Searider

Thanks all.

Prop does have a bush - I took it off last night and checked. The bush doesn't look chewed up.
Doesn't do it when the boat is heavily loaded.

Engine trimmed correctly I think.

Never had a prop hub tested - the few that have spun have been obvious.

Will experiment with moving weight around and see what happens.

Cheers

Duncan

When I was a little lighter and could get our little sib on the plane it was ventilating all the time, in out every few seconds. Slatted floor boats aren't supposed to plane it the reason really. Does it get on the plane with you on board?

[Downhilldai]

It's an Avon Rollaway, so not a slatted deck in the way gotchi & loco appear to be thinking. This boat has a deck made of interlocking (a bit like tongue & groove) panels, which form quite a rigid floor. In terms of rigidity, much nearer a plywood floor than an airdeck.
Heavy though

[jyasaki]

Grease pencil stripe on prop, insert, and rubber bushing should show if the bushing is letting go.

I'd lay odds it's due to lighter load when the kids are in it (not trying to say anything about your weight...)

Might throw a couple of sandbags in the back next time the lids are playing.

jky

[Searider]

Originally Posted by gotchiguy

When I was a little lighter and could get our little sib on the plane it was ventilating all the time, in out every few seconds. Slatted floor boats aren't supposed to plane it the reason really. Does it get on the plane with you on board?

Rated for 15hp - so I guess it should plane!

[Searider]

Originally Posted by Downhilldai

It's an Avon Rollaway, so not a slatted deck in the way gotchi & loco appear to be thinking. This boat has a deck made of interlocking (a bit like tongue & groove) panels, which form quite a rigid floor. In terms of rigidity, much nearer a plywood floor than an airdeck.
Heavy though

Bloody heavy to get in and out of the car!

I reckon the little Avon 260 RIB I sold was lighter - should have kept it!

[Searider]

Originally Posted by jyasaki

Grease pencil stripe on prop, insert, and rubber bushing should show if the bushing is letting go.

I'd lay odds it's due to lighter load when the kids are in it (not trying to say anything about your weight...)

Might throw a couple of sandbags in the back next time the lids are playing.

jky

Good idea re the prop.

It does plane with me on board and i'll admit to 90 something kg. I reckon the kids are more like 70 between them.

I'll get them to put the fuel and anchor etc in the stern.

[Locozodiac]

Don't know that brand model, but have it clear now about floor type, assume it has a standard transom, not a transom mount, right ? If so, could it be a long shaft transom and you are using a short shaft engine. If the transom measures 15"-17" it's a short one.

If 20"-22" with same engine + badly trimmed, or a combination of both, there's your aireation problem, assuming prop is working ok.

Happy Boating

[Searider]

Originally Posted by Locozodiac

Don't know that brand model, but have it clear now about floor type, assume it has a standard transom, not a transom mount, right ? If so, could it be a long shaft transom and you are using a short shaft engine. If the transom measures 15"-17" it's a short one.

If 20"-22" with same engine + badly trimmed, or a combination of both, there's your aireation problem, assuming prop is working ok.

Happy Boating

Definitely short shaft transom.

Will have a play with the trim.

[Locozodiac]

Trim & passengers must be set to have... when on plane :

Happy Boating