HP increase

All, please check my thinking…

Considering an electronic 60 HP upgrade for 1-2 knots when needed. I’m thinking if prop pitch stays the same and I add HP, will not be in danger and likely am slightly under propped?

Thanks

Does the higher rating change the rated RPM of the engine, or is it 60 more HP at the same RPM? If it's higher, you'll either be fine or over-propped after the change. If it's at the same RPM, you'll be underpropped and won't load the engine enough to use the extra power, so no extra speed.

Same rpm, @ 2,600. How would I know how much pitch to change?

You'll probably want 1 - 2 inches more pitch to use the extra power in that case. Try one of the prop calculators on the Michigan Wheel site and see what it spits out. Or talk to a local prop shop for ideas.



What size prop do you have now, what's your current WOT speed and current WOT RPM?

What engine(s) do you have. If Cummins QSBs or QSCs then it is pretty straightforward to electronically upgrade hp (for $$) as the mechanicals are the same. Volvos maybe and Yanmars probably not possible.

Any good prop shop can take your current wot rpms, add 60 hp virtually and see what effect that has on the prop and add or subtract pitch accordingly.

David

jimdavi said:

Same rpm, @ 2,600. How would I know how much pitch to change?

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for same RPM you'll need to increase pitch in order to increase speed.

if you decide to increase pitch and don't engage the additional HP you'll be over propped at most speeds without the additional 60HP.

Even with a large (unless 1000lbs+ removed from an electric car) the batts may only give a few min of added power.

If you can get to theoretical hull speed , 60hp will not push you far up your bow wave.

On a true displacement hull 2K may require double the installed power.

A better shot might be some sort of engine modification.

FF said:

Even with a large (unless 1000lbs+ removed from an electric car) the batts may only give a few min of added power.

If you can get to theoretical hull speed , 60hp will not push you far up your bow wave.

On a true displacement hull 2K may require double the installed power.

A better shot might be some sort of engine modification.

Click to expand...

I thought the op was talking about an engine software upgrade to get 60 more hp not a 60 hp electric motor. Maybe I'm misunderstanding someones post.

On a boat that size I would not bother. Ten miles at ten knots will take you an hour. At 11 knots you might arrive a couple minutes earlier. On an eight hour cruise the extra one or two knots would still be almost nothing.

pete

I sorta agree with Pete. A lot of money will be spent for a gain that will probably never be used. Now if you truly gain 2 kts, that’s a 25% increase and that could be significant on an 8 to 24 hour day. However, the fuel consumption to time ratio will probably prevent the use of this new found HP. I could see this if the SF current ran at 8kts but it doesn’t and I suspect you won’t even gain 1 kt from 60 hp.

Also, do you really want to run for long periods of time at WOT to try and squeeze that extra knot of speed out or it? 2knts sounds overly optimistic for +60hp on that boat.

jimdavi wrote;
“Considering an electronic 60 HP upgrade for 1-2 knots when needed.”

The answer to your implied question is simple. You never “need” more or extra power. You just plan for what you’re doing. Or if you’re not much of a planner (like me) and you’re approaching a tidal rapid you slow down on your way to the rapid or leave earlier in the morning making an adjustment as to when you arrive at the rapid. Or you go your normal speed and anchor, perhaps two miles from the rapid until you can resume your journey and arrive at the rapid at a better time. Much the same would happen w no planing at all. When you arrived at the rapid and witnessed or experienced the current you could take a little side trip (hopefully interesting or fun) until you could return to the rapid at a better time.

Obviously it’s a matter of how much planing one is willing to do to to achieve an acceptable outcome.

I’ve rarely done “buddy boating” but w a certain individual I did. We both had the same boat but my boat had about 20% more power. And the other variable was John and myself. John was the planner. He traveled via AP in a straight line and made his turns at pre-planned waypoints.
I chose the most interesting looking seashore (assuming there was one or two) and went there at 7.35 knots .. or 8.5 knots at times. I kept him in sight and never lost track of him. It worked well.
But he thought my “half assed” approach to navigation was stupid. And I thought his silly approach to navigation was a waste of time and unnecessary.

But one dosn’t need to get from point A to point B at a specific time .. just at an appropriate time.

In my years w a 6 knot boat I’ve only once encountered a real problem. That was when we lived in Thorne Bay and tried to go to Petersburg. Late fall or early winter. In order to do that we would need to go north through Wrangell Narrows. We had traversed Wrangell Narrows numerous times and didn’t consider it a big deal.
We went first to Coffman Cove. The weather was just acceptable. We had stern seas w 18-20 knot south winds and the run was mostly good. But as we got close to Coffman Cove winds and seas increased. We had a time of it after we turned west to go into Coffman Cove. The helm was very busy for a time but we got in and rafted to a 45’ aluminum fish boat. Good we got in when we did as it blew 45 knots all night long. Sideways rail and lots of it.
Then I actually did some planing. I discovered we’d need to transit Wrangell Narrows largely in the dark of night. Years before I worked on the Alaska state ferries and had seen the light show that is the lights of the nav-aids along the channel. What a sight that was. 57 lighted nav-aids and all the reflections on the water. Range finders and all.
We went home.

The limitations of winter cruising became painfully obvious.
But my near total lack of planing didn’t help much. So planing is a good thing. But a little extra speed would not have had any real effect on our failed run to Petersburg.

Bottom line is that your increase in power and 1 to 2 knots would only be of benefit in rare occasions. I have little idea how much benefit you’d get in the bay area. If you were to be able to transit one or two runs up or down the coast so-as to make such runs doable that may be an advantage. But I’ve been retired for quite a few years and go forth w that mindset.
Or perhaps you view this as mechanical/engineering fun. I wouldn’t overlook that value.

Nomad Willy said:

The answer to your implied question is simple. You never “need” more or extra power. You just plan for what you’re doing. Or if you’re not much of a planner (like me) and you’re approaching a tidal rapid you slow down on your way to the rapid or leave earlier in the morning making an adjustment as to when you arrive at the rapid. Or you go your normal speed and anchor, perhaps two miles from the rapid until you can resume your journey and arrive at the rapid at a better time. Much the same would happen w no planing at all. When you arrived at the rapid and witnessed or experienced the current you could take a little side trip (hopefully interesting or fun) until you could return to the rapid at a better time.

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From a basic trip planning perspective, I agree. But with a hull form that can take advantage of the extra power, there are situations it will improve boat handling or performance (even if it's not useful for getting somewhere faster). When running in a following sea, more power is often useful. With a planing hull, you can often make use of as much as you can get. On my boat, following seas are pretty much the only time I push the engines to max continuous (and sometimes still wish for enough power to get another 1 - 2 kts).

Nomad Willy said:

jimdavi wrote;
“Considering an electronic 60 HP upgrade for 1-2 knots when needed.”

In my years w a 6 knot boat I’ve only once encountered a real problem. That was when we lived in Thorne Bay and tried to go to Petersburg. In order to do that we would need to go north through Wrangell Narrows. We had traversed Wrangell Narrows numerous times and didn’t consider it a big deal.
We went first to Coffman Cove

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Eric,

What am I missing? what was the problem?

backinblue,
Not enough light in the day to get as far as one needs to get at times.
In Juneau there’s only about 3hrs of daylight in the winter and it’s flanked by semi-darkness. Running at night in the winter in SE is way different than in the summer. And I seldom run at night then.
Did I fill you in? Glad you asked as others probably missed it too.

If you have a buddy with a small boat with about a 100hp outboard you might have him tow you at your WOT to see if there is any useful speed increase.

Nomad Willy said:

backinblue,
Not enough light in the day to get as far as one needs to get at times.
In Juneau there’s only about 3hrs of daylight in the winter and it’s flanked by semi-darkness. Running at night in the winter in SE is way different than in the summer. And I seldom run at night then.
Did I fill you in? Glad you asked as others probably missed it too.

Click to expand...

Yes, thank you, makes sense now.