18 Chieftain with 75 Honda; prop ideas?

[Nissan_Ranger]

Hello, folks.

I'm new to this site and I see a LOT of older Starcraft Chieftains here. I've got a mid-seventies 18 foot Chieftain cuddy with a Johnson 85 Seahorse fuel guzzler. It all came to me very reasonably priced and I'm re-powering with a brand new Honda 2010 75HP four stroke. The old Johnson pushed the craft up to 35 MPH (by GPS). Do any of you have ideas on what the right prop might for the Honda?

N_R

 

[steelespike]

Re: 18 Chieftain with 75 Honda; prop ideas?

Welcome,35 from your 85 seems pretty respectable.
I'm certainly no Honda expert but near as I can tell Honda makes an excellent motor.
I'm not sure its best to go with less hp.From my limited 4 stroke knowledge their weak point is hole shot and they require careful prop selection for best performance.Starting out 10 hp down
I don't know?? Your 85 is about 288lbs the Honda 359 like adding a small person right on the transom.While this is surely a prop question its possible the best prop guess might come from the Honda Forum. Also your dealer should know where to start and let you try props till its right.
I believe there is a Starcraft forum possibly here at iboats there may be some prop suggestions there.
What is the hp rating of your boat?

 

[Nissan_Ranger]

Re: 18 Chieftain with 75 Honda; prop ideas?

Hello, Steelespike,

The C/G plate says the maximum allowable power is '150'. I too had reservations about the hole shot of a four stroke. Some of the reviews I read about the new Honda 75 have lead me to believe that the 75 has enough low end grunt to do a respectable enough job, this being due mainly to computer controlled timing and fuel injection. Nothing I have read about matches the E-tech two strokes for hole shot, but the price of this deal was too good for me to turn down. Interesting to note that the only significant mechanical difference I've been able to figure out between my 75 and the 90 is the electronic controlled variable valve timing which kicks in over 5000 RPM. I'm not a speed demon by any means

 

[Bob_VT]

Re: 18 Chieftain with 75 Honda; prop ideas?

Well....this may be some good news for you. Depending on the year of the old Johnson 85 ....you can expect just about the same performance. If your Johnson was a 1983 or older then it was a motor with the HP rated at the head and there was about a 10%+ loss at the prop...... do in theory ....the old 85 was actually putting out about 76.5 HP at the prop. The Honda is a prop rated motor and it is putting out 75 HP at the prop. Confused yet

Did the Honda come with a prop? I would probably go with a 17" as a start and see where the boat performs from there.

Welcome to iboats!

 

[Nissan_Ranger]

Re: 18 Chieftain with 75 Honda; prop ideas?

Thank you!

The old Johnson is a mid-seventies engine which makes it the lower rating. I did know there was a change in all that somewhere along the line; thanks for clearing that up for me as I wasn't certain where the old engine fit into that. The old Johnson worked perfectly except for being a smelly fuel guzzler. I plan on retiring in the next few years without much in the way of pension and I want this new Honda to be reliable and economical to operate with reliable being the key word.
The deal includes fitting for a prop although I'm going to do a ten hour break-in before doing a final fitting.

 

[Bob_VT]

Re: 18 Chieftain with 75 Honda; prop ideas?

With the exception of a weight change I image you will be good to go!! Let us know how it works out.

 

[Nissan_Ranger]

Re: 18 Chieftain with 75 Honda; prop ideas?

With the exception of a weight change I image you will be good to go!! Let us know how it works out.

Well, today the hourmeter read 6 hours when I docked at the boat ramp. Four hours left in the break-in period and 8 1/2 Imperial gallons (38 liters) of fuel gone through my new motor. I was present for the engine install and things got done to my satisfaction. Only time I stepped in and interfered was when they wanted to take it out after the install and do the prop check right away. No way were they going to rev my new engine to it's max on it's first run. Book calls for idle trolling/speed for the first 15 minutes and no more than 3000 RPM for the next 3/4 hour. So I took it from them (My money, my motor, my rules!) and did an hour and a half of break-in before letting them do the prop check. Anyway, I got it up to 33 MPH in rough water. Motor did it at 5500 RPM and has the 17 pitch prop on. Seems good to me.

 

[steelespike]

Re: 18 Chieftain with 75 Honda; prop ideas?

Was the 5500 with your typical load?
Usually they prop close to the max rpm(6,000) with a 4 stroke.As long as you can test props
a 15 might improve overall performance without sacrificing top end.
Usually a lower pitch will improve hole shot and the ability to stay on plane with less diddling.
Getting to speed easier is a fuel savings.

 

[Nissan_Ranger]

Re: 18 Chieftain with 75 Honda; prop ideas?

Was the 5500 with your typical load?

Boat was typical with fuel and two people.

A 15 might improve overall performance without sacrificing top end.
Usually a lower pitch will improve hole shot and the ability to stay on plane with less diddling.

The old boat rockets out out of the hole. Whatever Honda did to get that sort of lower end performance is amazing and the drop off as RPMs increase I attribute to three things: The engine is designed for low-end torque AND the V-tech add-on which makes the engine a 90 horse, the boat has a fairly large light freeboard in the form of its boxy, aerodynamically inefficient cuddy with upper windshield and bimini and, finally, there are no trim tabs. It is getting trim tabs; I'm tired of sitting at weird sideways angles every time I have a different load or side wind.