Which engine?

[km1125]

You're not going to get more than hull speed out of that engine, regardless of the gearing. You might be able to get another knot or so, but I don't think much more than that.

What kind of RPMs does the engine run? What size prop do you have?

[bud37]

Source of the post mjk1040, Good morning, you do bring up a strong case which the diesel. I really do like the diesel. I just wish we could get more speed. I’m lucky if we can get 6.7 knots out of her at full throttle. I can’t go full throttle with her because she starts to overheat. I’ve gone through the raw water cooling system. Next, I’m going to make sure the inlet on the hull isn’t clogged. If memory serves me correctly, the transmission on the engine is 1.51 to 1. The Walter v drive says 1.88 to 1. If anybody has any suggestions on how I could tackle this, I’m all ears. It could be something as re-gearing. I know 65hp is not much, but I’d like to maximize all the potential for this boat.

Welcome to the forum Jim....

My take here is, your 65hp diesel is more than enough to run your boat along at what is referred to as hull speed.I don't believe in this case changing gearing and props will do much of anything and here is why I believe that. Now I am not any sort of marine engineer here, just been around boats for a while.

Because it is a planing type hull maybe around ( my guess ) 23ft waterline length, really at 6.7 knots you are probably already digging a hole and pushing water, with the boat now trying to climb the bow wave. So considering that, there would be a good reason for the engine temp to climb as there is no way it can push any harder. Planing hulls are not very efficient at slow speeds, my guess here is to keep it around 5 Knots max for your length boat. Planing hulls are by design good on plane at speed and for the most part more inefficient than a displacement hull at slow speed.

Now consider the alternative, you want the boat to plane and go much faster.....that will require an engine package to replace what you have there now with all the attendant pieces to change all from diesel back to gas. I doubt this expense will be recovered at all in the end with that year boat and may, as has been mentioned, cause some unforeseen issues to crop up.

My two cents Jim....... I like the little diesel actually, should be quite economical to run......

[Oldie]

Re: your over heating problem at full throttle...
Your diesel engine will spin much slower than a gas engine at the crank. Did the previous owner allow for this and gear the impeller pulley/drive accordingly?

Also, diesels' tend to run hotter under normal use..... is your temperature gauge calibrated for a diesel engine?
Just points to ponder.