Upgrading engine hp

[jswwrites]

Our new (to us) boat has the original Universal 16hp diesel, by all accounts in great shape. However, it's a 16hp engine on a 33 1/2' boat with a 9500lb displacement... At the time the boat was built, that was the 2nd lowest of the 4 engine options. My husband would like to upgrade to at least a mid-20s hp engine.

Now, before you say "you're supposed to be SAILING"... The boat will be berthed in Beaufort, NC, and the ICW both north and south for a fair distance is not sailing water, and we will be doing weekends in these areas. We have sailboats go by our house by the dozens every day, obvious live-aboards, boats from Oriental, etc., and I have never once seen one with a sail up. So to GET somewhere to sail, we will have to motor a pretty good way, and we'd obviously rather not add one day for every 3 in the process!

So, with that said, two questions:

1. Advice on brands (I know Yanmar is "it", but others?)?
2. How do you figure out the optimum hp without going past the point of diminishing returns? Since Newports aren't made anymore, we can't ask them!

[Faster]

Wow - 16 hp is a bit light for a 33 footer - can lead to real problems motoring in rough conditions.
Since you already have a Universal I'd suggest you stay with them for an upgrade. Universal is pretty good at maintaining the same footprint for mounting, offering near drop-in replacements.
If you go to Yanmar, Volvo or whatever you will probably be looking at moving motor mounts, modifying stringers etc all of which makes the job much more complicated and expensive.
Besides, I've found Universal engines to be generally quieter than Volvo and some others.
It's still a bit of project - a bigger engine will likely require shaft modifications as the package will be longer and the coupling in a different location.
We have 48 hp on 34 feet/11,500 displ, a bit much perhaps, but handy at times. There's a happy medium between 16 hp and what we have!

Any manufacturer will likely have info on hp vs displ., and the prop suppliers can help you there as well.

[Gene T]

Spend money if you want, but the first thing I would do is get the full HP out of the engine you have. Most sailboats have inefficient props and don't run at the peak engine HP. In order to reduce drag sailboats typically use 2 blade props with small blades. As it is a sailboat preference is given to sailing drag over motoring power. A small prop spends a good portion of its energy heating up the water rather than pushing it. For about $300 you could put on a 3 blade power boat prop. Sizing one is tricky but you want to just reach WOT while motoring at speed. You will then want to drop about 200 rpm for most motoring. You may find you can get effectively 20-30% more power out of your current engine by just putting on a more efficient prop. Find a local prop shop to work with. One expensive compromise would be a folding 3 blade if you can find one to fit.

[jswwrites]

The boat has a folding prop, as they raced it locally (back in the day!). My husband knows a lot about props for powerboats (who knew there was so much to know about props, anyway?!)...but if we do have the folding 3 blade now, can we do much better?

[camaraderie]

Let's take a step back here for a moment. If we use a waterline length of 30 ft. which I think is generous, your maximum hull speed with ANY size engine is 1.3 times the square root of 30 or 7.1 knots. How fast do you go now in flat water? If it is close to 7 knots which I suspect it is...do you really want to spend $15k on a new engine? Of course if you are bucking heavy currents the extra HP might be worthwhile but I just want to make sure you understand the speed limits of the boat regardless of engine size!

[jswwrites]

I think it's 27' at the waterline... And we do have some pretty hefty currents. That is my husband's main concern, being able to maneuver and dock the boat in weather and current. We could theoretically get in trouble right in front of our house, although we won't be docking there -- it's probably only 175' across the ICW and the current is swift. I have to pull our Robalo (power) into the lift at a 90 degree angle to the current and it is quite the experience, with a much more maneuverable boat. Going further up into the Adams Creek area, before the Neuse River, the water is even more unforgiving as the ingoing tide meets the river/Pamlico Sound movement. So I think he's just like to know we had enough to get through all this area where sailing is absolutely not an option... And an extra 1-2mph on a longer trip adds up over time, as a secondary consideration.

[Gary M]

How fast do you go in flat water? If you are about hull speed then more power will not help even in current. Where it does make a difference is in rough water where more power or a better prop will keep your speed up.
If you have a folding prop, try a fixed 3 bladed it will make a big difference in both directions.

The prop manufactures such as Martec or Gori can be contacted on line with boat and engine details and will give a promt recomendation. Not a lot of cost either and I bet you will be pleasently surprised.

Gary

[Gene T]

First I would want to see the power curve for your engine, look in the owners manual. It shows the HP at various RPM. You want to be able to run in the high HP range. It is common for boat owners to over-prop their boats, kind of like overdrive, to conserve fuel. But this limits the amount of power the engine will put out but only gives you hull speed in calm water.

So run your boat into a strong headwind with a sharp chop and see if you can run close to WOT. If not you can just re-pitch your prop, something like 150-200 RPM/inch. It depends somewhat on how good the folding prop is too. More blade area is required for efficient HP delivered to pushing the boat. For best power delivered in a displacement boat, use the largest diameter prop that will fit and then the correct pitch to reach WOT (wide open throttle) under the worst conditions (highest load).

[jswwrites]

I'll give my husband that info. Quite honestly, I don't know how fast it will go in flat calm water as the knot meter has been broken for about 20 years! (When I asked about it, the friend of my grandmother's who has been maintaining the boat for her said, "Just see how long it takes you to go between markers and divide it out." Well yeah, but a quick look would be nice, too! Seems to me, from my recollection of my times on the boat, it used to go maybe 5 or 5 1/2 knots under power.

[Gary M]

A knot meter is useful, the time between markers only works if there is no current. There and back and average it will come close. However you can just get some one with a similar size boat to run along side of you and tell you how fast you are going. You need this info before you consider doing any thing else.

A decent speedo is only $2-3 hundred.

Gary