Stringrays are they wort it ?

[Basil2]

G'day, I have a 4.5mtr staccer centre console(hull 1986) with a 2003 2 stroke mercury on the back. What the problem is that it seems to cavitate very easily. The motor is set on the bottom hole on the transom,with the cavity plate above the prop sitting approx 60-70mm below the haul and the top plate about 70mm up the transom. These measurement are when the motor is fully trimmed in,would a stringray mounted to the motor leg help with the cavitation problem ? Any help would be appreciated. Regards Basil2.

[seatime]

Don't Stingray foils help the boat plane easier, not sure if they will help with cavitation.
Why is it cavitating with the cav plate 60-70mm below the hull, something sounds amiss there. What's the top plate that's 70mm up, that you refer to.
Have you checked that the bush in the prop isn't stuffed, can't see why it cavitates if the cav plate is below the hull.

any pics

rgds

[RayB]

I have done a lot of research lately on correct motor, and I am far from an expert but I think your motor is too low on the transom. I am also surpised it is cavitating but the motor should be lifted so that the cav plate is in line with the bottom of the hull or maybe fractionally below. This is only a general rule and will differ from boat to boat. Trial and error may be needed.

cheers
Ray

[Basil2]

There are 2 plate up from the cavity plate,these are part of the casting of the leg. There purpose in life I am not sure. The boat planes quite quickly if your heavy handed on the throttle. I have checked that the prop is on firmly. I'll post a pic tomorrow. regards Basil2

[Angla]

Sounds like the motor needs to be brought up so the bottom cav plate you are talking about is nearest to level-to 1 inch up-with the bottom of the hull.
I have a merc 135 on a 575 outsider and found that the stingray I put on has reduced the cavitation remarkably. Turning corners is vastly improved now.

Quite often I find when you take off that you wan't to go the other way but you would have to be careful as to how much power you used. Now I find I can accelerate and turn as hard as I like. That is useful when bar crossing.

Angla

[Angla]

Found another

[BaysideMarine]

Hard to tell from those pics Angla but it looks like your engine is mounted too high.

Your cav plate needs to be level with the keel for a fibreglass boat or level with the lowest part of the typical keel extrusion on an aluminium boat.

If, on an aluminium boat the cav plate is level with the lowest part of the keel extrusion cavitation should not be an issue and a hull deformity would be expected. If no hull deformity could be found, then fitting of a cupped propellor will significantly reduce the incidence of cavitation.

I have found cavitation to be a regular problem with aluminium boats....... Don't often see it on fibreglass boats....

Cheers,

Nicholas

[goat]

looks too high too me.
cheers

[Chimo]

Hi
Your motor looks to be too high.but its hard to say from the photos. Also where is your trim set?

If things are set up correctly, and someone else drives while you stand at rear and look at the fin:-
1 when you take off the foil will be under water
2 as you gain speed and trim motor out at medium to high cruise top of fin should be almost out of water and
3 at high speed cruise in a straight line, heading towards fast and towards wot with motor trimed out further you should be able to almost fit your fingers between the bottom of fin and water surface

Fauilure to fit motor correctly, ie too low, will give you drag from foil at higher speeds. The eratic boat behavoir people are reporting from foils is more than likely due to the foil / motor being too low and grabbing which would also have affected top speed.

Foil is there to assist at low to med speed not needed at high speed as hull is supposed to do the lfting at that point

All boats I have had foils on, old frp swiftcraft with 100hp, 10 tinny with 9.9 12 tinny with 9.9 HP and 5.6 m Al cuddy with trim tabs and 100Hp and 6.2 FRP with tabs and twin 115's (fin on each) have all been better out of the hole with minimal to no loss of top end speed with motors lifted to correct height.

The stingrays being mounted as far back as they are should be easy to get out of the water at the medium to higher speeds due to the extra trim angle

Looking forward to the next chapter in your story

Chimo GOM

[Basil2]

I have taken some pics,however I haven't been able to post them. However I noticed on the pics of Angla's boat that my motor sits considerably lower in the water than his. With my cav plate sitting at least 70mm below the haul of the boat. I will probably buy a stingray and try it and see if it helps me like it did Angla. Thanks Basil2

[RayB]

I have taken some pics,however I haven't been able to post them. However I noticed on the pics of Angla's boat that my motor sits considerably lower in the water than his. With my cav plate sitting at least 70mm below the haul of the boat. I will probably buy a stingray and try it and see if it helps me like it did Angla. Thanks Basil2

70mm for the cav plate below the hull sounds way too low from the research I have done. I know we were telling Angla that is motor is too high but you have opposite problem. I would strongly suggest getting the motor height right first before buying a foil. My motor was sitting 40mm below the hull and I raised it by 40mm this week and tested it today. Raising the engine has given me before shot out of the hole, faster speed at WOT and higher rpm at WOT. I had a foil on my motor which I have now removed!

Here is a pic of my current boat height. If you are having trouble loading a pic of motor height don't forget to resize the pic so that it is less than 100kb

[7dan7]

looks to high to me

great pic rayb shows exactly the cav plate height

cheers dan

[Basil2]

Thanks for the advice RayB, I'll take it on board and give that a go. By lifting the motor ther will be a gap between the top of the motor clamp and the transom,will I need to put a spacer in place to take up that gap? Still can't post pic, not the greatest with the old computer skills, have resized pic to 89kb however still must be doing something wrong. Regards Basil2

[-spiro-]

motor looks low to me? and i rate the se sports fin better than a stingray 8-)

[Angla]

Thanks for the concern there fellas. If I had the SE sport fin off and trim the motor to level with the keel, the cav plate falls somewhere between level with the keel and 1 inch above level. It is hard to take a photo of this as the fin and the leg block the view of the keel in a photo.

I am happy with the performance I get and have seen that the fin rides above water height during higher speed travel. I believe it helps me to turn and keep power on at the same time, stopping cavitation.

Angla