Avon 620 propping

[Avon620]

Hi all, I have an avon 620 rib with a yamaha f150. My rib is overpropped because
at wot the most i can achieve is 5300 rpm and run 48 mph gps. Also I cannot trim more than half (on my command link gauge) because when I trim more the handling becomes very bad. I would like to have your suggestions for a new prop because in my country the prop shops don't let me test the prop before I buy.

I've been reading posts here and all say that the avon have the bow very light, and mine have some extra weight at the stern because it has a grp spoiler fitted with stainless steel. I uploaded an album called avon 620 if you wish to see it.

Now I came with a conclusion that I need a prop that provides good stern lift so this will balance the rib and will help to avoid the problem that it has the bow too light. Do you think that I am right? Also I would like to have some prop suggestions or maybe share your prop results and advantages.

Thanks all!

[Exe treme]

Hi I am not an expert on the prop question, and I am sure there are experts on the forum to help with pitch, diameter, material etc. However, I have re-propped a few boats over the years, with both higher and lower pitch, and it sounds like you need to go to a lower pitch prop. For example, if you are currently running a 19 degree, try a 17. I did the same on a 6.2m sports fisher - it made a lot of difference to acceleration and helped to get the nose down quickly. Top end suffered a little, but only by about 4mph.
The only other suggestion is to consider if the GRP spoiler is creating downforce at the stern, in the same way that a spoiler on a F1 car does. A stainless A-frame doesn't affect the airflow much, but a wider spoiler might.

[Avon620]

Thanks for your reply, you only dropped the pitch of the propeller or you always change the brand/style? If dropping pitch will help to get the bow down I will try to borrow a yamaha black stainless in 19 pitch. The fact of the downforce is interesting but I don't know how I can check this. If you think you can consider it from a picture, take a look at the album I uploaded yesterday called Avon 620.

Thanks

[Nos4r2]

What EXACT prop do you have fitted at the moment?There's only one diameter for an f150 if I remember rightly so Pitch, number of blades, material.

Use it as a benchmark and only change ONE of the above at a time.

I wouldn't go much more than a 2" pitch drop, in the same material and the same number of blades. Your recommended WOT rpm from yamaha is 5000-6000 so you're already in that band, and you hit full HP delivery at 5500rpm.

[Avon620]

The prop I am running right now is a yamaha black stainless steel 13 3/4 x 21 M.
I know I am in the good rpm as the owners manual say but many people say that if you don't get the yamaha f150 as close to 6000rpm she will make oil. And I'm not sure if mine is making oil or no because the oil level was about 3/4 of the dipstick and now it's over the H. I am thought that maybe the oil filter oil has come down the oil pan but I don't think that it's the reason.
Thanks

[jyasaki]

Making oil generally happens when idling along for long periods of time (think slow trolling with fishing lines in the water.) Thought to be due to a decent amount of cooling water through the head, with minimal heat generation due to the low firing rate. Oil cools off to the point where gasoline blends with the oil, as the temp isn't high enough to flash it off. Giveaway is that the oil smells pretty much as gasoline does.

If the oil is milky/foamy and does not smell like gasoline, you have other (more serious) problems.

jky