Surtees 4.85 with Yamaha F70 motor

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    Posted: 28 Feb 2015 at 1:33pm
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Hi everyone.
I have been on this forum a couple of times and picked up a few pointers from time to time. This is great. Keep up the good work.
We have just in November 2014 bought a new Surtees 4.85 and had a Yamaha 70hp four stroke motor fitted to it. Mostly we are very happy with the boat apart from some issue as can be seen in the video clip I attached.
As you will see when we are on the plane and we gradually start to slow down to a stop a “stern wave” starts to develop behind the motor with the end result of the water being dumped on the motor as high as the air intake, located near the top of the motor.With this issue I cannot take a chance to do an aggressive (quick) stop as then the “stern wave” will actually run over the top of the motor, which happened once before, and water entered the air intakes of the motor. We have tried a number of different motor positions (trimming) all with the same results. At all times, all the weight (people and gear) was in the front and the gear stowed in the bow of the boat. Fuel on board ranged from half a tank to three quarters of a tank (tote tank).
We are not newbie’s to boating and have owned a couple of boats before the Surtees but we never experienced anything like this before. I would hate to think what will happen if we have a big following sea and I do a stop.
Before purchasing we did a sea trial on a 4.85 fitted with a Yamaha F60 and none of this was visible. The reason for going with the 70hp is because we have 2 sometimes 3 scuba divers with gear on board and the extra grunt helps.

Here is hoping that there will be someone out there that can help solve the mystery


http://youtu.be/kLfaaYJP8Yc

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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 2:29pm
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Looks like the motor is set to low on transom as even on plane plate above prop not that visible? Very strange looks like a standing wave almost what do Surtees say?.

Unrelated question - am looking at repowering my boat and Yamaha F70 interests me compared to F60 as higher hp and almost same weight due to extra valves etc - you say you tried a Surtees with a F60 and went to F70 for more grunt - is their really a noticeable difference as F70 is quite a bit more money?
Good fishing trip nothing breaks, great trip catch fish.
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Post Options Post Options   Likes (0) Likes(0)   Quote HB_fishdive Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 3:11pm
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Off topic, is the f60/70 for the mac?
I have a f60 on mine and I wish i had a few more horses on the back
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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 3:14pm
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Yes I have a Merc 50 2 Stroke 9 yrs old (still reliable) thinking of repowering and going to Merc 60 but wondering about F70 as same weight though more expensive - other 70 -75s are heavy unless 2 S.
Good fishing trip nothing breaks, great trip catch fish.
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Post Options Post Options   Likes (0) Likes(0)   Quote Olfart Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 3:20pm
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I agree with MacSkipper re the height of the outboard on the transom.  It looks very like the height of my outboard on my boat and I reckon mine is mounted a tad low.
Semper in excreta sumus, solum profundum variat....



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Post Options Post Options   Likes (0) Likes(0)   Quote otdrmn Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 5:37pm
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I have a surtees 6.1
IMO you need to lift motor 1-2 holes, the cavitation plate should be just skimming the surface when motor fully trimmed out, your water line seems to be at the second plate.
What is the max rpm your pulling at the moment?

The 4 R's ~ Rods, Reels, Rifles, Rooting
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Post Options Post Options   Likes (0) Likes(0)   Quote otdrmn Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 5:45pm
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Video of my motor running here - just uploading now so give it a few minutes
The 4 R's ~ Rods, Reels, Rifles, Rooting
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Post Options Post Options   Likes (0) Likes(0)   Quote yknot Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 8:14pm
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Did I read you have tote tanks? Could it be too much weight in the stern?
I have a 5.5 (with under floor fuel tank) when I run long range and have tote tanks in stern the boat is shocking, have changed to putting fuel up front and back to normal ride conditions.
Go back and discuss with the agent you bought boat from, the Surtees agents I deal with are great.
Those that say it can't be done are being overtaken by those doing it.
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Post Options Post Options   Likes (0) Likes(0)   Quote lemmy Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 8:36pm
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Originally posted by MacSkipper MacSkipper wrote:

Yes I have a Merc 50 2 Stroke 9 yrs old (still reliable) thinking of repowering and going to Merc 60 but wondering about F70 as same weight though more expensive - other 70 -75s are heavy unless 2 S.


Ever thought about a 2 stroke 90 yammy same weight and heaps more grunt.

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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 8:41pm
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Not considered a 90 2 Stroke though I can see where you are coming from - not wanting to overpower boat but also interested in 4S efficiency, quietness and low smoke/fumes.
Good fishing trip nothing breaks, great trip catch fish.
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Post Options Post Options   Likes (0) Likes(0)   Quote lemmy Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 9:14pm
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I,ve got a 60 Merc Bigfoot but a seriously looking to trade to a 2 stroke 90 Yammy those things a bullet proof and go well.

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Post Options Post Options   Likes (0) Likes(0)   Quote Don18025 Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2015 at 9:48pm
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Motor is not high enough and to much weight aft.
Tell us what the boat loading is for this video? two tote tanks aft and 4 scuba bottles???
I would consider the 485 a two diver boat (4 bottles, gear & boatman) not 3 divers (6 bottles, gear and boatman).
Was the Sturtees ballast chamber full or empty for the video?

You may wish to work out the trim of the boat a little better. Move some weight forward, r trim engine.
The stern wave should not harm the motor, and it looks as if it has no show of entering the cockpit...so the boat is safe, but not doing the job efficiently. Nice engine and hull
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Post Options Post Options   Likes (0) Likes(0)   Quote sixpack Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 8:36am
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Thanks for all the feed back. Here is to answer questions in feed back so far.
The motor is set to the correct high, according to the dealer, as they have done many of these set ups before ( according to him). I have been out on a sea trial with the owner of the dealership, I did it my way and then I slowed down to a stop (taking even longer)the dealers way, and the stern wave was a little bigger. The dealer advised me to consider fitting a hydrofoil, but I can not see why this should be done as it is a new package and it should perform normal is it was supplied. I sent the clip to Surtees and it seems like they not sure why this is happening but they (surtees and dealership) told me that that sort of thing is common on boats under 5 meters with the 20 inch shaft. Now they are happy for me to swap to a 60hp motor at no charge. Here is the thing, the 60hp and 70hp motors both have a 20 inch shaft....I am confused???
My max revs on the motor is about 6000/6100rpm.

Yknot....who was the agent that you are talking about?

At this stage we did all the testing never with more than half to 3 quarters of a tote tank. That will be the only weight aft. All persons(2) and weight was up front and gear was in the bow area. At this stage I have not had any dive gear or divers on board. I have tried the trimming of the motor in different positions but with no difference to the stern wave. I have had the ballast flooded and empty with the same results. I am not worried with the water coming into the cockpit area as this will not happen. My concern is the water going into the motor via the air intake.

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Post Options Post Options   Likes (0) Likes(0)   Quote kaveman Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 8:46am
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Motor definately looks too low, lift it a hole and trial that
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Post Options Post Options   Likes (0) Likes(0)   Quote Get in behind Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 9:43am
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I had the same model surtees with Suzuki 60 with totes. They weigh almost the same as the yamaha. I never had any issues as you describe.
It did perform better with weight up front. Usually had two on board as well as fishing gear.
The only thing I can think of is your outboard pod isn't sealed, therefore you're losing about 50 kilos of buoyancy.
Great boats though
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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 1:15pm
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Interested in dealer comment about permatrim (hydo foil) - I have one on my Mac 420 and it makes an amazing difference - gets up and flies along - but cannot imagine it would fix what you are seeing as it is most effective at speed.

Could you post a picture of motor in running position on trailer with hull visible from side so members can comment on height compared to their Surtees boats just in case dealer is mistaken and motor is to low?
Good fishing trip nothing breaks, great trip catch fish.
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Post Options Post Options   Likes (0) Likes(0)   Quote Olfart Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 1:37pm
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I took a clip off the video for my own purposes so here is a copy.  Clearly shows Cav plate too low in the water....

This will be creating drag and is exactly what I am experiencing on my boat (different boat though).  Will also cause excessive fuel usage as the engine will be working harder than it should be.

Semper in excreta sumus, solum profundum variat....



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Post Options Post Options   Likes (0) Likes(0)   Quote sixpack Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 4:45pm
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I also thought the motor is to low but on doing the calculation for the motor height I calculate mine to be 33mm and it is about 31mm (for every 300mm that the pod extend away from the stern the cavitation plate on motor should be about 25mm above the bottom of the hull).

"Get in behind"...you mention about the pod not being sealed. The dealer also went on about it but the pod is sealed and bone dry as well as when removing the bungs on the outside of the hull.

Olfart...about the fuel consumption. I am not to sure as I have not used the boat that much....at this stage I am concentrating on the motor more than watching the fuel.

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Post Options Post Options   Likes (0) Likes(0)   Quote Olfart Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 6:18pm
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sixpack - I understand what you are saying, but that formula for outboards mounted on pods probably differs with each boat design so at best I reckon it can only be taken as a guide to initial setup.  A setup which suits one boat will not necessarily be right for another boat so adjustments are necessary.  I have already had my outboard raised by one hole and the difference in the before and after performance was quite marked. 
After having done about 30 hours with the current setup I am finding the outboard is still not achieving the manufacturer's recommended rev range - so for me, raising the outboard by a further hole on the mounting bracket should help to achieve that - which will put the cavitation plate where it should be when fully trimmed out.  (Doing the same on your boat could have a better effect on the "stern wave" you experience when slowing down as there should be less drag in the water.)
For me, from there it will be a matter of calculating the ideal "prop slip" for the rev range and theoretical speeds for my outboard should be achieving and then matching that against actual speed recorded.  If there is a marked gap between ideal prop slip and actual prop slip then changing the propeller to a different pitch and/or size should make a difference.
Check some of the earlier posts on this subject - particularly those by Steps who has a real good handle on this - and you will see how important it is to get the setup right for your boat.
Semper in excreta sumus, solum profundum variat....



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Post Options Post Options   Likes (0) Likes(0)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar 2015 at 6:37pm
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Sixpack - I had to play with my boat when I got it as motor was to high on transom - the clue was that the trim when adjusted at speed did not work properly because motor was not right height - eg calm day with normal load cruising speed - trim motor in pushes bow down - right in it should "bow steer" and pull and dig in, trim motor out and boat bow should lift - motor will blow (cavitate) if gets to high and bow while start to porpoise (bounce) .

Does your motor trim between these at cruising speed? Weight distribution, tote tank location will effect so some degree as well - when motor was to high I could not get bow to push down with trim in and motor would cavitate and porpoise far to easily. Once motor height dropped it changed and would do both - then I looked at props and changed to get performance I wanted.

Reason I say this is you should be somewhere in the sweet spot in between and should have sufficient trim so you can go move motor either way to compensate for load, sea conditions speed etc.

I am not exactly sure (others may know) what effect prop has on this, in my experience prop effects getting out of hole, cruising and top speed and hold in corners - but I believe what I said about trim applies unless prop is way out of ball park.

Maybe others can comment on this while I duck for cover!
Good fishing trip nothing breaks, great trip catch fish.
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