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Is my Honda 150 hp over propped?

Neville

New member
Hi
I bought the boat last year - a 640 C Bar Crusher when it was fitted with a Solas 14.25 X 17 X 3 prop. It seemed way under propped.
As a result I bought a Power Tech 4 blade which has made a huge difference. Only thing is that WOT is at the bottom (about 5200 rpm) of the recommended range in the Honda manual which is 5000 - 6000 rpm.
The rev counter is analogue so not exactly sure of accuracy.
Got the following results with GPS when testing both props.
The Honda seems to run very easily at between 4000 - 4500 rpm - the V boost kicks in at about 4300 rpm - with the Power Tech. The table shows the results. Am I likely to damage the engine by persisting with the 4 blade Power Tech prop?
Regards
Neville

Honda 150 BF Serial no. BANJ 1006573 2006 year
Revs
Power Tech (kmph)
14.25 X 17 X 4 - PTZ model
14.25 X 17 X Solas (kmph)
3000
16 (just planning)
18
3500
31
24 (just planning)
4000
41
30
4500
45
37
5000
53 (max revs -possibly 5200 with a bit of tinkering with trim)
44
5500
-----
54
6000
-----
58
 
Personal opinion - Assuming that the boat was about the same weight during both tests, yes, you are over prop'ed with the Power Tech. But it also looks like you may be under prop'ed with the Solas.

The Power Tech props have a great reputation. Perhaps dropping down to 14.0 inch diameter will give you a good in-between.
 
A solas 19 pitch will bring it down under 6000 around 5600 wot. Rule of thumb is 200 rpm per inch of pitch. The only way to tell for sure is real time on the water. How well does it pop out of the hole with the power tech?
 
All your results include a tach you do not trust the tach use a tach timing light and see if the tach is correct. You can probably borrow a timing light tach at your local autozone.
 
The Solas prop is slipping badly. Prop slip at 4500 rpm is 32% and slip at 6000 rpm is 20%. I would assume the motor revs quite freely and it takes time for boat speed "catch" up to engine speed. The lack of bite is allowing the motor to turn more rpm.

The 4 blade power tech slip is much lower. Slip is 12% at 5000 rpm. In my opinion the 17 pitch power tech is too much prop for your boat. You could drop 2" pitch and go to a 15" and pick up around 400 rpms.

You may want to check the mounting height of the outboard. The anti-ventilation plate should near the surface of the water after the boat is planed out. If the motor is mounted too low it causes unnecessary drag and raising the motor will increase rpm a little.
 
Hello
Thank you for the prompt responses to my question.
Looks like I need to get a slightly "smaller" prop.
The boat is fairly heavy - I think about 2000kg when fuelled up with 300 litre of petrol. It also has a water ballast system so a lot of water has to drain out to get it up on the plane. The Power Tech prop made an amazing difference with the hole shot and had the boat planning very quickly. Whereas with the Solas although the revs go up quickly the boat takes a long time to get moving and up on the plane. Sorry I don't have times but there is a remarkable difference between the two props. I have lifted the motor up one hole as the anti-ventillation plate remained covered with water when at WOT and trimmed right up. Never done this before and turned out to be a lot easier to do than I thought it would be. Will get out on the water next weekend to see what difference lifting the motor makes. I am thinking to take advice given and go to a 15" pitch Power Tech although they do have a 16" pitch version. Have included a pic so you can see the boat configuration. Again thanks for the advice, Neville
Bar Crusher 640 C.jpg
 
Hi
Went out last weekend and was pleasantly surprised to get an extra 500 RPM at WOT from just lifting the motor one hole - conditions on the water were a bit rough so not a good opportunity for testing but certainly highlighted the need for getting the motor position correct, cheers Neville
 
A 500 RPM increase from raising the motor one hole is significant. That increase should put you WOT RPMs close to where they need to be. Did the prop loose grip or ventilate any in the rough conditions?
 
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