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BarraMan the 200 HP is to much weight for the DE25. The DE25 is an easily driven boat that Jacques designed for lower HP traveling. As he said he wants to keep motor weight around 375. A 115 will drive this boat at cruising speeds very easily. I am a little puzzled also as the Study plans say 200HP while Jacques is now saying 375lbs. Maybe he can explain? It might be the difference between 2stroke and 4stroke weights?
Kyle in my research the HO Etec's have the same HP as the non-HO. The difference is they put a larger bottom gear ration on them. For example the 115 has the same shaft HP of 115 for both the HO and the regular one and the same displacement of 105 cubic inches. The only difference is the final gear ratio 2.44 for the HO vs. 2.25 for the regular 115. You will be able to put a larger prop on but you still will be limited by the HP. The Suzuki DF140A has a final gear ratio of 2.59.
I can do the calculations but right now we are looking at a weight of 2489lbs, 1800-2000 for the hull and around 390 for the motor for a total displacement of over 4700lbs.
Am enjoying watching your build, and hope this helps a little.
Regards, Tom
Last edited by TomW1 on Tue Oct 06, 2015 2:45 am, edited 1 time in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978
Tom, I was just giving my opinion. It's worth what was paid for it!
My science background has trained my brain to question what doesn't compute well for me. I struggle to see that an extra 100ibs down the back of a 2000lb boat is gonna make a big difference. May not cruise quite as economically as designed but the OP has said that is not the major consideration.
Listen to Jacques. He designed the boat. If you build it and power it as designed, it will perform as designed. Again, whether you but a 90 hp on it or a 130 on it, it will not "wallow", regardless of your weight (assuming you don't put all the weight on the transom) The heavier boat will use more gas and not go as fast, but it won't "wallow".
Disclaimer: I would prefer to see the boat kept below 4,000 lbs displacement and stay with the 115 engine but this is a special use boat with divers, gear etc.
99% of DE23/25 builders will use the boat for cruising and don't have to worry about more HP and weight.
I ran some figures:
Let's discuss speed and HP first.
The boat is designed for a displacement of 2,800 lbs but I expected builders to build heavier or load the boat above that figure.
One builder (David Sours) posted performance figures and he estimates his displacement to be 3,750 lbs.
From there, we can extrapolate using the Crouch formula.
(Tom, if you play with that, set C = 170).
From his figures, I can also see that the engine is developing about half its nominal HP at 4300 rpm.
Now, I increased displacement to 5,000 lbs and the formula tells me that to get 27 mph, we need 115 HP.
That is at WOT!
Let's run the engine at 4200 rpm and estimate that we get 1/2 nominal HP,
speed is 18.3 mph.
You are still on plane and at 4200 rpm, you have a good reserve of power.
The boat will fall of plane at about 4,000 rpm.
All this is speculation, I should look at the engine manufacturer power curves but since I do not trust them 100% we could just as well estimate.
Now you see why I trust a 115 even for a heavy load.
If I try with a 130 HP (the HO), we get 19.4 mph at 4200 rpm.
Let's compare to a 200 HP running at 4200 rpm (I assume = 1/2 max. HP = 100), speed = 24 mph. At WOT = 34 mph.
34 mph is too much for that boat. The transom will be fine but the bottom will not like it . . .
Do not compare the behavior of the DE25 to an overloaded small Carolina Skiff.
The Skiff is either on plane or bogging down at 5 mph pushing an ugly wave.
The DE25 can move very decently at intermediate speeds (semi-displacement speed) like 12 to 15 mph.
Enough speed to have good steerage and avoid broaching.
With your weight and speed, I recommend to add to the bottom, one layer of biaxial each side for up to 130 HP and 2 layers if you go above 130 HP.
Trim and cockpit depth.
Let's assume that, at rest, the bracket will support most of the engine weight = only small change in trim.
As designed, at 2,800 lbs, the top of the cockpit sole is 1.5" above the DWL.
With a PPI of 600 lbs, at 5,000 lbs, the cockpit is more than 1" under water.
To keep the same drainage safety margin (1.5"), we should raise the cockpit by 2.5".
(PPI increases as WL goes up because of the flare).
Plus, with all the weight, I would love to see a 4 or 5" bridge deck at the cockpit frame. We don't want water going inside.
A drop panel in the companion way is a minimum.
To raise the sole is easy: sister the stringers under the cockpit. That means add a layer on each side and fill the void.
The cockpit will still be deep enough, we start with 28" and can give up 3".
For the running trim, you should move as many weights forward as possible, we discussed that.
Bottom line, I would go for the 115 HO because this is not the same hull than the Carolina Skiff.
Keep in mind that you will not need to run at 27 mph to avoid broaching and that you will not always be loaded to 5,000 lbs BUT
If you feel better with more HP, do it.
I am surprised by the small difference in engine weight but you are correct, I saw the Etec online brochure.
Try to build the boat light. We discussed foam sandwich for the superstructure and I strongly recommend that. I can revise the scantlings for the foam given on the plans, we can save a few pounds there.
Same for the cockpit sole and decks; Make then from honeycomb or foam and you'll save a couple hundred lbs total.
Again, this is not an endorsement of a bigger engine, only some recommendations about how to handle the extra weight and speed.
Thank you very much Jacques! This eliminates our fears of being underpowered. The 115HO should increase the range of the boat over a 200HP too with the same fuel supply as well. I would not mind at all having to step over the raised bridge deck if it means making the boat more seaworthy and raising the sole would actually be beneficial to visibility out of the cockpit when people are sitting in beanbag chairs back there. Also thank you David for the info on the smooth transition up on to plane. Most boats I'm experienced with have to overcome a large bow wave when loaded heavy to get up on plane. Its very exciting to know that this boat doesn't.
Wow Jacques, what a great and thorough clarification/explanation. Marschall, that transition is truly remarkable. For 35 years, I only knew boats that were either displacement or had to climb out of a hole to get on top. The DE 25 has none of that. It defies everything I ever knew. It's maybe the coolest aspect of the design.
Kyle I'm still having a problem seeing where you get 130HP for the HO Etec. Can you show me where you get that. The Evinrude manuals show shaft HP as 115 for both the HO and the regular motor. The difference is the higher gear ration on the HO which is 2.44 which will allow you to put a little higher pitched prop on the HO.
Regards, Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978
Tom i think he is looking at the 135 HO which is built on the v6 block and is actually putting out 148 HP.The weight
is 433 LB with a 25" shaft. The 115 HO is 415 LB but i don't know the rated HP on this one and its a V4 .
I am a little puzzled also as the Study plans say 200HP while Jacques is now saying 375lbs. Maybe he can explain? It might be the difference between 2stroke and 4stroke weights? 
