Volvo penta AQ280 Mounting height

Hello

I have bought an old fiberglass speedboat with an AQ100 drive leg. I want to change it to a more modern drive. I have bought a second hand AQ280 drive. However I am wondering what the best mounting height is on the transom before i cut the hole. To prevent drag or prop cavitation.
Most of the pictures online of AQ280 plates put the underside of the boat just above the anti cavitation plate at the narrow point of the leg. I was also wondering if the height makes a difference for the noise coming from the exhaust. Also the plate curves upward slightly towards the rear.
I hope some people with some experience with mounting these drives can chime in.

Thanks in advance

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Rimmert said:

Hello I have bought an old fiberglass speedboat with an AQ100 drive leg. I want to change it to a more modern drive. I have bought a second hand AQ280 drive.
The standard 280 does not incorporate PT, plus it incorporates the dreaded Reverse Latch system. There is a 280 PT (if you could find one), but parts may be hard to find these days.
A more modern drive (while staying in the AQ series family) would be a "C" or later drive.


However I am wondering what the best mounting height is on the transom before i cut the hole. To prevent drag or prop cavitation.
This is commonly referred to as the X dimension.
The hull's dead-rise may affect this dimension.

Most of the pictures online of AQ280 plates put the underside of the boat just above the anti cavitation plate at the narrow point of the leg. I was also wondering if the height makes a difference for the noise coming from the exhaust. Also the plate curves upward slightly towards the rear.
I hope some people with some experience with mounting these drives can chime in.
See if any info here helps you.
https://www.google.com/search?q=how.....0i22i30k1j33i22i29i30k1j33i21k1.4drTQeAPY1g


Thanks in advance

Click to expand...

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Re: Exhaust noise with 280 drives...

When the boat is on a plane, the drive " planes" on the lower edge of the cavitation plate (assuming the correct x dimension), leaving the exhaust port itself totally exposed. 4 banger noise not all that bad. As I recall, the 100 drive had an exhaust port that was exposed when hull on a plane.

Thanks for the replies

My Volvo is just the Standard AQ280 no trim or anything fancy.
I have used the height from looking at photo's of other AQ280s. And the way i have it on my boat would probably leave the exhaust port slightly underwater. Most boat seemed to have it installed that the top of the plate is equal to the bottom of the hull. Sometimes slightly lower. I have used this dimension give or take..

I cant seem to find the mounting bolt however. I have found only 12mm bolts or 16mm bolts, An ideal fit would be a 14mm bolt but I cant find these in the proper version. I could use a 12mm bolt but it has a lot of play in the transom plate. I dont know know the inch sizes, (I live in Europe that's why in Millimeters) There are official volvo penta bolts but there seem terribly expensive and I still wouldnt know if these fit properly.

The transom shield mounting bolts are Galvanized US 1/2" N/C carriage bolts. Not metric!
In fact, most all of the AQ series fasteners are US N/C threads.

BTW, the are at the square bore for the carriage bolt head does not make the water seal.
The water seal is accomplished with the 6 special "Fat O-Rings" that fit around each bolt shank.

These Fat O-rings become compressed against the bolt shank via the tapered (counter-sunk) hole within the actual transom.
If your transom bores are not slightly tapered, you will want to taper them!

Aaahh so they're called carriage bolts in english... I was wondering about that. I believe 1/2" would be a fraction bigger than 12mm But that still seems like a rather untidy fit so to speak. For the bolts I thought that metric vs US threads wouldn't make alot of difference. Is is not a problem then if the fit through the transome plate is rather loose? With al the forces and the weight of the engine hanging on there i would feel more comfertable with a snug fitting bolt in the transom plate.
I am slightly worried that it might even be able to shift a couple of millimeters in a tight turn at speed with the force of the propellor pushing.

Like said........ 1/2" NC thread carriage bolts.
Purchase the ones with NO THREADS near the carriage head! In other words..... ones with a smooth shank in this area.

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The offset of the cav plate from the hull bottom is not a constant. It varies with boat size/type. I have a copy of the dealer installation drawings/procedure for the 280 drive. If you would like, I'll scan them to a pdf file and email them to you. Just give me your email address via a pm (private message).

sandkicker said:

The offset of the cav plate from the hull bottom is not a constant. It varies with boat size/type. I have a copy of the dealer installation drawings/procedure for the 280 drive. If you would like, I'll scan them to a pdf file and email them to you. Just give me your email address via a pm (private message).

Click to expand...

Bob, would you mind posting the images in the Volvo Penta archive section?


Meanwhile, I just realized that I had this image :

Will do...

Sorry for the delay. Can't find a way to post to the Archives. While looking thru files, realized I had a number of dealer install manuals ( including: power steering, hydraulic steering, prop selection, wiring...etc.) from the early 80s. The local dealer got tired of answering my weekly questions and loaned me all his manuals to copy. I contacted the site administrator to suggest adding a "Library" section since the Archive is disorganized. Haven't heard back as yet. Soooo.... see below.


OK.....View attachment Volvo_Transom_Layout_270-280.pdf

RicardoMarine said:

Meanwhile, I just realized that I had this image :

Click to expand...

Rick regarding transom shield sealing: it looks as if the rope seal and O rings do the entire job. On my '86 Bayliner with AQ131a/275, the factory applied some sort of sealant around the entire perimeter of the shield. Of course, after 30+ years, it has become brittle and is pulling away in spots from the transom. Given that the rope & O-rings provide the main protection, would it be at all advisable to scrape away the old sealant and replace with.. 5200 or similar? There is currently no leakage whatsoever through the transom shield..