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Old 14 July 2013, 07:47   #31
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Bump!
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Old 13 October 2013, 16:06   #32
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Help!!!

Right!

I finally got round to buying the Solas 11 x 15 propeller to replace the OEM 11.1 x 13 Tohatsu one.

I fitted it today and unfortunately I have to say I am very gutted! =( I am getting bad cavitation, think that's what it's called where the water comes splashing up behind the transom. It never used to do that with the old prop! Also my WOT rpm with just me in the boat has now gone from 6000 rpm on the rev limiter to 5000 rpm!!!! and my max speed is down 2 mph too!

Why on earth have I lost 1000 rpm?! I was expect a reduction of 300 - 400 rpm by going up 2" in pitch (with an increase in top speed!) and also I was not expecting bad cavitation if that's what the splashing I am experiencing is called. I will do some research now but thought I'd ask you guys first! Do I need to raise my motor up one hole to stop this cavitation? TBH I don't want to do this and don't think I will be able to, if I had known this would have happened I would have simply stuck with the OEM prop! Hopefully I can get a refund if this isn't going to be a simple fix!

I appreciate your help, thanks!
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Old 13 October 2013, 18:05   #33
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At risk of being rude James we gave you the advice and help and worked out that your set up was as near as dam it as good as it can be . Put the original prop on and back off the last few hundred revs when alone in the boat . Small boats are so sensitive to load /rpm you have to compromise a bit .
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Old 14 October 2013, 09:36   #34
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Ian I decided to change the prop because of the general opinion I got from this and other threads and also from speaking to boating/propeller experts on the phone.

Also something I didn't say in this thread; last time I used my rib I used a pressure gauge I had recently bought and found I was under inflating the tubes, and after inflating the tubes properly the boat was slightly faster when loaded and revving slightly more, it would rev to 5900rpm with 2 people!!! This is why I bought a bigger prop, to bring the revs down slightly! I hated the fact my engine was hitting the rev limiter and over revving. I shouldn't have to back off the last few hundred rpm.

Anyway back to topic, does anyone know what/why I am now getting this splashing?

I am with my boat for 3 more days and if I cannot sort this then the OEM prop will be going back on!
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Old 14 October 2013, 10:59   #35
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The problem is, that if You change both make of propeller and pitch, outcome will be complete guesswork, the design differences between various brands is so big. I noted this on my tohatsu 25 and also recently on my 90 yam(same pitch, big difference in performance).

Go with the stock 11x13 or borrow another 11x13 , black max, solas, that might make the trick!
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Old 14 October 2013, 17:05   #36
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Quote:
Originally Posted by C-NUMB View Post
The problem is, that if You change both make of propeller and pitch, outcome will be complete guesswork, the design differences between various brands is so big. I noted this on my tohatsu 25 and also recently on my 90 yam(same pitch, big difference in performance).

Go with the stock 11x13 or borrow another 11x13 , black max, solas, that might make the trick!
I'm surprised at what you say, but at the same time agree as it makes sense!

Also the Solas prop looks identical to my OEM one and also I have been told by a couple of different propeller specialists now that Tohatsu no longer actually make their own props and I must admit my OEM prop looks identical in how it is made and the style to the Solas prop! I have also noticed that Solas are the only prop manufactuer that sell the exactly the same diameter and pitch sized props as Tohatsu have in their prop chart! This is also a coincidence! Lastly I read somewhere on the internet that Solas make the Yamaha props and someone told me that Solas make some of the Tohatsu ones.

Either way the style of the two props I have look identical, so I am shocked I have lost 1000 rpm for a 2" pitch increase!

Also whilst I am here, I refitted the OEM prop today and I now think the splashing as I call it is not a problem as it is similar with both props, just slightly worse with the slightly higher pitched Solas prop!

As for speed, the sea today and yesterday has been flatter/calmer than normal and I have noticed before that in dead calm seas my max speed is a couple of mph less than when there is a bit of chop/waves. Well yesterday with the Solas prop I hit 38mph @ 5000 rpm (WOT) and today I hit 37mph @ what looked like virtually 6000 rpm but wasn’t quite 6000 rpm as the limiter was not kicking in (the water was dead flat this evening!) This miffed me until I remembered that my rib goes faster with some waves, only 2mph faster. I thought I would mention this as it shows that the solas prop was indeed 1mph faster at 5000 rpm than the OEM prop. I am just miffed at my WOT loosing 1000 rpm with it though!
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