etec 90 on avon 5.4 prop

[mcinfantry]

ok, swapped to a 90hp etec. all speeds gps measured.

ran today a couple hours. the motor is 20" all the way down and trimmed all the way down the cavitation plate is even with the bottom of the drain hole, not the keel. also, the motor is mounted in the original holes, DEAD center in the transom.

i have a 13 1/4 x 17 stiletto stainless steel propeller. i can get 4700 rpm and 39mph with about 40 liters of fuel, and 3 occupants. i have converted center console and leaning post.

if everyone moves to the back of the boat (except me) and ducks down out of the wind we could hit about 4900 rpm and 41mph.

according to the prop calculators, at 15% slip my prop is actually about 20.62". so to get 5200 rpm with a 15% slip i would need a 19" propeller.

i took the low-end on the slip... high end is 30% and the 17" is actually around 25". and i would need a 20" propeller.

i plan on adding a ice chest/seat in the back so i can fish in the thing. but that adds weight, and i also plan on adding a trampoline top to keep the sun from killing me.

my questions.
1) i realize my boat motor needs to be moved starboard about 1.5". would i expect any rpm increase/decrease?

2) what should i do on the propeller? go to a stilleto 15"? get mine custom reworked? change brands? or keep running it as-is. is it bad the motor will not go above 4700?

im not really concerned with speed, just hitting 5200rpm, or should i care?

[Chris]

with a 90HP Etec on a 5.4 searider I am suprised you are only getting 40mph.

MattH's old Searider with a 90hp Yamaha got close to 50 MPH.

I would say you need to look at your set up as something is amiss.

Also are you sure you GPS is displaying speed in MPH and not in Knots?

[mcinfantry]

Originally Posted by Chris

with a 90HP Etec on a 5.4 searider I am suprised you are only getting 40mph.

MattH's old Searider with a 90hp Yamaha got close to 50 MPH.

I would say you need to look at your set up as something is amiss.

Also are you sure you GPS is displaying speed in MPH and not in Knots?

well, i remounted the engine 1.5" starboard today and moved it up one hole. i was tempted to go two, but cant find anyone who has run two holes up. i hope to run it tomorrow

[mcinfantry]

huey, when you say third hole, do you mean third as counted from the top, or from the bottom? when i am one hole up, that means i am on the 3rd hole from the bottom of the 4 holes, i can raise it two more before i am out of adjustment.

i ran it today for 35 more miles (56 yesterday) and with 26 gallons gas, 2 up, we got 42~43mph.

day 1, 3 people, 12 gallons fuel, the trim gauge showed about 3/4 of the way trimmed up. 4700rpm and 39mph

day 2, 1.5" starboard, 1 hole up, 26 gallons fuel and the trim gauge was slightly above the "tick" and 42~43 mph 4900~5000rpm. if i trimmed up to yesterdays mark it would lift the nose slightly higher and "chine walk"... trimmed back down it kept speed.

where should the anti-ventilation plate be in the water??????

heres a picture of mine. you cannot see it at all when on plane at 4900~5000rpm. should i go up another hole?

[Nos4r2]

You're actually about right with 42-44mph given the amount of gas you're carrying. With 132 litres aboard (32 US gallons) and 2 people I make 36 knots or 42mph. Weight (and its distribution) is quite critical too-with a load of camping gear in the bow a few weeks ago I couldn't pass 32 knots.

Take it for a run with just yourself aboard and 12 gallons and you'll be surprised at the difference it akes.

[Chris]

Mcinfantry I would lift it another inch or maybe even 2.

The chine walking you are experiencing is one indicator that the engine is still too low.

[mcinfantry]

Originally Posted by Chris

Mcinfantry I would lift it another inch or maybe even 2.

The chine walking you are experiencing is one indicator that the engine is still too low.

im trying to find some riders!

thanks for the response! im less than 30 minutes from lake maurepas (91 square miles).

[reinier]

Originally Posted by Chris

Mcinfantry I would lift it another inch or maybe even 2.

The chine walking you are experiencing is one indicator that the engine is still too low.

Yeah I agree, chine walking in a boat like that with just over 40mph won't happen when it's set up right.

[ian parkes]

you are getting the same revs etc as i did with a 17" prop . I now have a 15 and its revving where it should . top speed hasn't changed but holeshot and midrange is much better . main difference was the fuel consumption improved a lot with the lower pitch prop , i think making the motor labour with too higher pitch makes it use lots more fuel

[mcinfantry]

i wonder if my tach isnt off..... anyway, im going to try a 15" pitch. maybe a 4 blade, it ran 40 with 3 today, and on 3rd notch. ventilates in turns more than i like.....