OUTBOARDS

[Jono Garton]

I AM LOOKING AT BUYING A RIB, THE YAM I AM CLOSE TO BUYING HAS ITS OUTBOARD BRACKETS (THE UPSIDE DOWN L SPAPE BITS THAT HOOK OVER THE TRANSOM ???) SITTING ABOUT 2" UP FROM THE TRANSOM. THE GUY I AM LOOKING AT BUYING IT OFF SAYS THIS IS FINE TUNING. WHATS YOUR OPINION?

ALSO WHEN I ENGAGE THE ENGINE INTO FORWARD OR REVERSE THEIR IS A VERY SMALL CLUNK ! I HAVE HAD THIS BEFORE ON OUTBOARDS. THE GUY I'M BUYING IT OFF SAYS ITS NOTHING (THE ENGINES STILL UNDER WARRANTY AND HAD ABOUT 20HRS USE). WHATS YOUR VIEWS?

[Alan Mckewan]

Moving the engine up the transom a bit was commonplace on sportsboats & racing boats, but is seen less often on RIBs. It can increse the boat speed by reducing the engine wetted area with the right sized (usually bigger than noraml pitch) prop. It is also done sometimes make an ender-revving engine increase its revs without buying a smaller itch prop. The problem with going too far up the transom on a RIB (even with the right bigger prop) is that when you turn hard a RIB tend to ride up out of the water more than a conventinal hard bottom boat as it immerses the collar. This causes cavitation which can be very severe, particularly on wide body RIBs.
As for the clunk in gear, no real problem, could well be made worse by swinging too big a prop. Probably better to get a smaller prop and drop the engine back down unless you are thinking of racing!

[Didier]

Hello from sunny Florida, recommend yamaha 115 4-stroke. I have 5.75m and with dive gear
tanks, guns, coolers and 3 divers, we maintain a steady 35 knots in 1m seas.
Good luck, yes I am new to ths web forum, CIAO Didier

[Jono Garton]

Got the RIB it handles just fine with the engine as it is, i will have a look at the prop see what pitch it is but the engine is not reving more than 5500rpm full on.

As the clunking you can't ear anything now it in the water and theres a bit of tension on the prop.

Spent 4/5 hours at between 3500 - 5500rpm and used £10 worth of fuel.

Why didn't i buy a RIB & a four stroke earlier?

[Alan]

Sounds good. If I do 4-5 hours with my 150hp 2 stroke and 6.5m RIB I burn between £60 and £80 of fuel!

Al.

[tsunami]

I wouldn't worry to much about the fact that the engine sits slightly high on the transom, this can actually be quite common as you have already been told.
What is more important is the position of the cavitation plate (the flat plate above the engine). On a standard setup this plate is normally in direct line with the bottom of the hull. If a boat is setup for racing this can be substantially higher than the bottom of the keel. Sometimes but rarely the plate is slightly below the line of the keel.
I would recommend for better all round boating that you keep it level with the bottom of the keel!
As for the clunk going into gear. Again this is quite normal and is more noticable on engines with stainless propellors due to the extra weight involved.
5500 rpm is also perfectly Ok.

------------------
Joe

[Chris]

I love finding old posts like this one....


Sorry Jono could not resist

BTW hope that clunking noise did not get worse