Prop wash

[Club 56]

Vision 42 2013

Can anyone shed some light on the amount of prop wash they experience under power.

Ours I would say is high to very high. Especially at anything over 1800 RPM"s

Boat came with factory fitted Volvo D55 and a Volvo 3 blade folding prop.

Cheers
Club 56

[Salty]

I think to make a meaningful comparison, it would be helpful if you could provide a little more information such as for example, but not limited to :-
Propeller size,
Fixed or folding blade
Whether variable pitch or not
Are you the original owner from new, and if not whether the prop was standard issue for the boat,
What sort of speed the boat achieves at 1800 rpm in still water on a calm day
Whether you have any significant hull fouling.

[Symphony]

How are you defining propwash? Is it causing interference with the rudder so deflecting the boat such that you need to correct with steering to keep the boat straight? Generally saildrive boats do not suffer much from this because of the separation between the prop and the rudder. If it is specific to a narrow rev range then avoid running at that setting.

[Yngmar]

You mean prop walk? Because prop wash is quite good to have for turning the boat in place and other close quarters maneuvers.

https://www.sailnova.com/2018/04/19/prop-walk-vs-prop-wash/

[Club 56]

Thanks for your replies.

OK, I call it prop wash over the rudder, perhaps it's prop walk.
My issue is it's very quick to turn sharply to Starboard if I let go of the wheel under motor. Happens in 1-1.5 boat lengths. Going forward.
Motoring at around 6-7 knots 2000-2300 RPM,.
Prop was factory fitted and I beleive it to be a Volvo 3 blade folding. Unsure of ∅.

Cheers
Club 56

[Symphony]

Turning to starboard going ahead is what one would expect from a LH prop which Volvo saildrives have, although as I suggested earlier normally this is not pronounced because of the distance between the drive and the rudder and the closeness of the drive to the pivot point of the boat. Your non standard prop may well behave differently from the standard fixed 3 blade. Hopefully somebody with the same boat and a standard prop will comment. It is not unusual for different propellers to have different characteristics in this respect. On one of my previous boats (not a saildrive) I changed from a fixed blade to a feathering one and the latter had a strong pull to starboard going forward.

Don't think there is anything you can do to actually change it so it is a case of finding ways to compensate. It can be tiring when steering by hand and constantly keeping pressure on the wheel to port, although this can be eased by tightening the wheel lock to increase resistance. It is easier if you use the autopilot when motoring as this will automatically compensate for the bias and keep to your compass course.

[Rampage]

Do I understand correctly: under power if you let the wheel go the boat turns sharply to starboard?  So, the wash from the prop hitting the rudder causes the rudder to go hard over and turn the boat sharply?  I’d expect that or similar to happen to any boat under power as the turbulence from the prop will push any rudder off to one side or the other.  A balanced spade rudder (as fitted to the Bavaria’s) will then complete the movement and remain there until it is brought back to amidships by the wheel.
To stop it happening, you could either engage the autopilot or tighten the wheel brake so as to resist the effect of the turbulence.

[Salty]

This might not apply to your boat, but was a situation I saw last year where I was asked to visit another yacht where they had a similar problem of the vessel apparently wanting to veer off to starboard when driving ahead. On taking a look at the situation onboard I found that the wheel had a marking on the rim to indicate when it was amidships, but it didn’t seem to me to be in the right place. Setting the wheel mid ships according to its marking and locking it in place, the electronic rudder indicator was indicating the rudder to be amidships, but going down into the lazarette and taking a look at the quadrant, the rudder was actually some 5 degrees or so off to starboard. Looking at their autopilot system where the hydraulic ram connected to the pin on the quadrant, it was found that the pin was such a sloppy fit, that I was surprised it hadn’t all separated and parted company. Apparently some time earlier in the year the wheel had become disconnected from the quadrant when one of the steering cables broke, and following a temporary (now long standing) repair it had become apparent that the wheel marking was no longer the mid ships position, and so the electronic helm indicator had been used to determine the mid ships helm position. It wasn’t right, and nobody had thought to take a look into the lazarette to check the true position of the quadrant. In consequence they were going around with a little bit of “right hand down a bit” which they didn’t realise !!

Sometimes you have to see the unthinkable to realise that for some it actually happens !!