Double Eagle -need to tweak prop pitch or settle with pretty good

Designs for inboard or outboard power

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North
Posts: 265
Joined: Mon Jul 15, 2013 6:29 pm
Location: Nova Scotia

Re: Double Eagle -need to tweak prop pitch or settle with pretty good

Postby North » Fri Aug 04, 2017 6:18 am

seems like it so far, but I have not tested it a lot yet. long story, but I had steam / water / coolant in the exhaust at the start of this season -about 2- 3 weeks ago- talked to some experienced mechanics (marine and auto) and per normal, folks thought it was the head gasket or a cracked head. I did NOT try removing the exhaust manifold as I assumed it had perhaps been on there for 25 years and figured I would break bolts / need torches. etc.. So, I removed the head with exhaust manifold and turbo still on it - but, the head gasket looked good and noticed what looked like cracks near injectors and valves in 2 cylinders...started looking for used/ new heads and then finally took manifold and turbo off of head- found that the gaskets between water injection plate on manifold were in very bad shaped and looked like signs of coolant passing into exhaust chambers. while the exhaust ports on the head looks dry. cleaned off head more and "cracks" turned out to be previous weld/ machining repairs - so put all back together with new gaskets and it seems to be working fine.
In hindsight, in the auto world, water/ coolant in the exhaust typically comes from head gasket or a cracked head...as there aren't other points for coolant to enter... but on marine engines with water cooled exhaust manifolds and water cooled turbos, these areas/ gaskets are also likely suspects... Had I checked them first I would have got away with 1 or 2 gaskets and a couple of hours of work vs maybe 15 hours of work and a whole upper gasket kit the way I did it.....

have not wanted to push it much but it seems to "top out" at about 21 kts, where before I got 23 kts - but I get 21 kts at 2600 rpm where before I needed 3300 rpm to get 23 kts - and 3300 is well beyond recommended maximums of 2500rpm continuous and 2800 intermittent use.

In hindsight, If I had not increased the pitch, or only by perhaps 1 inch, I could likely hit 2800 and maybe see a higher top speed - in the end though, I will likely spend most time at between 2200 and 2500 rpms so at around 18- 21 kts in this range, I am pretty happy. I think the chop will likely keep us below 20 kts on many days anyway - I would have liked to have the potential for 25 kts intermittently - may be out f reach now, as against your thoughts.... i did go with heavier plate and some heavy steering brackets, etc so I may have ruled this out - overall though, the boat is rugged and I am still happy with the 3/16" bottom and sides vs 1/8" plate - thinner would have been more challenging welding and trying not to warp from heat...and I had enough challenges....

User avatar
kens
Posts: 4388
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Double Eagle -need to tweak prop pitch or settle with pretty good

Postby kens » Fri Aug 04, 2017 9:17 am

On marine engines, the exhaust manifolds are often accepted as expendable items, they corrode so bad.
The wet elbow is , for sure expendable.
In your case, there is the possibility that you may get more rpm if you get good head, manifold & turbo all sealed up and proper tuning.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:


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