Engine height

lightning · 08 August 2009, 18:31

I've got a Zodiac 285s SIB and Mariner 6hp engine. The instructions for the engine state that the anti-ventilation plate should be 1-2 inches below the bottom of the boat. on my boat it's just under 3 inches...is it worth fitting a spacer to raise the engine an inch or will it make no difference?

lightning · 09 August 2009, 13:42

Oh, sod it....I'll just put a 1" spacer in and see what happens.

lightning · 09 August 2009, 16:04

I've just assembled the boat on the lawn and I don't think there's any point messing with the engine height. At just over 2 1/2 inches it's less than 1 inch lower than the recommended range of 1 to 2, but the engine instructions say "bottom of boat" and on a SIB the bottom of the transom is not as low as the bottom of the tubes/air keel anyway....so I'm not sure it's going to be that critical.

astra · 09 August 2009, 16:50

hello,you have a set up allmost the same as mine next time i am out i take a picture of engine to bottom of boat for you to compare,have got it to go any faster yet ?

lightning · 09 August 2009, 17:06

Hi there, I've only been on the canal so far with it, but I have opened it up a bit on a stretch of canal going past a factory where the sides are made of steel plate. (so the wash won't cause damage)
The boat easily makes 5mph according to my GPS with well under half throttle. After that, more power just raises the front/lowers the back of the boat and causes a large following wave. The speed only increases to about 5 1/2 mph!
I'm going to Windermere next week so will try it there. I mean it's just the standard Zodiac 285s with the Mercury 6hp, the same as everybody else buys, so it can't be "faulty".
The engine trim is set at no.3 (no. 1 being closest to the transom) I tried it at no. 2 and it did not seem to make any difference.
I've seen videos on YouTube of these boats doing 10-12mph and they look the same as mine. Same engine, even the 4/5hp versions which are identical to look at and the same weight.

astra · 09 August 2009, 17:19

Quote:

Originally Posted by lightning

Hi there, I've only been on the canal so far with it, but I have opened it up a bit on a stretch of canal going past a factory where the sides are made of steel plate. (so the wash won't cause damage)
The boat easily makes 5mph according to my GPS with well under half throttle. After that, more power just raises the front/lowers the back of the boat and causes a large following wave. The speed only increases to about 5 1/2 mph!
I'm going to Windermere next week so will try it there. I mean it's just the standard Zodiac 285s with the Mercury 6hp, the same as everybody else buys, so it can't be "faulty".
The engine trim is set at no.3 (no. 1 being closest to the transom) I tried it at no. 2 and it did not seem to make any difference.
I've seen videos on YouTube of these boats doing 10-12mph and they look the same as mine. Same engine, even the 4/5hp versions which are identical to look at and the same weight.

Mine is set on number 4/5 with a tiller extension on and just me it will plane easy,when the front rises move forward,tiller extension is a must or long arms,mine is a 2.7m airdeck so shouldnt be to much in it.

http://www.youtube.com/watch?v=MwCe8...layer_embedded

lightning · 09 August 2009, 17:57

Your engine trim is on no. 4/5.....would that mean the engine is tilted forward (prop further away from the boat)
If I set mine to 4/5 that would certainly be the case.

astra · 09 August 2009, 21:06

yes sure is

lightning · 10 August 2009, 00:00

I'll give it a try.
How far below the bottom of the transom is the ventilation plate on your engine? I guess it's probably similar to mine. Sounds like you might have the same engine, it's a Mercury but also comes branded Mariner and Tohatsu.

GandyGoose · 10 August 2009, 10:15

Hi,

Same engine here, I think. Mine's a four-stroke Mariner 6hp, on a Zodiac Zoom which is actually a RIB but very flat at the stern. I made a hardwood block to raise the motor just over an inch, and I've alternated between trim fully down and one notch back.

Regarding performance at full power, ours is very slow to get on the plane with two on board, but it does get there. Initially the stern digs in an the engine sounds like its labouring, but then gradually it accelerates and the revs rise. It makes a very anti-social wash while accelerating. We have seen 14kn with two on board once up to speed.

lightning · 16 August 2009, 12:33

Went to Windermere this weekend, seems Like I was worrying too much! Out on the (fairly choppy) lake a brief burst of full throttle with 2 of us on board saw 14.5mph on the GPS.
I say brief as the speed limit on Windermere is 10mph (6 in places).
Opening the throttle it does take a few seconds to get going.
The large wash at about 5-6mph clears and the boat then increases speed rapidly.

Locozodiac · 16 August 2009, 18:33

Quote:

Originally Posted by lightning

I've got a Zodiac 285s SIB and Mariner 6hp engine. The instructions for the engine state that the anti-ventilation plate should be 1-2 inches below the bottom of the boat. on my boat it's just under 3 inches...is it worth fitting a spacer to raise the engine an inch or will it make no difference?

If your zodiac has 40 cm measured from upper transom to sib's bottom transom will be ok if using Mercury/Mariner/Nissan/Tohatsu engines, if not, under 39.5 -38 cm, might experiment water splashing inside sib, correct heights parameters improves performance with less water drag/splash issues on tail.

Happy Sibbing